feat: Konzerte button on artist page (Android)

- EventModels: ConcertEvent / ConcertVenue / ConcertOffer (Kotlinx Serializable)
- EventsClient: Ktor client fetching backendUrl/api/events/{artist}
- ArtistViewModel: fetches events in parallel with iTunes data on load;
  openEventsSheet / dismissEventsSheet
- ConcertsSheet: ModalBottomSheet with event rows (date, venue, city,
  Tickets → button that opens browser, Ausverkauft state)
- ArtistDetailScreen: Konzerte pill in action bar showing event count,
  tapping opens ConcertsSheet

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

android/app/src/main/kotlin/com/novasonic/app/api/EventsClient.kt

@@ -0,0 +1,26 @@
+package com.novasonic.app.api
+
+import com.novasonic.app.api.model.ConcertEvent
+import io.ktor.client.*
+import io.ktor.client.call.*
+import io.ktor.client.engine.android.*
+import io.ktor.client.plugins.contentnegotiation.*
+import io.ktor.client.request.*
+import io.ktor.serialization.kotlinx.json.*
+import kotlinx.serialization.json.Json
+
+object EventsClient {
+
+    private val http = HttpClient(Android) {
+        install(ContentNegotiation) {
+            json(Json { ignoreUnknownKeys = true; coerceInputValues = true })
+        }
+    }
+
+    suspend fun fetchEvents(backendUrl: String, artistName: String): List<ConcertEvent> {
+        if (backendUrl.isBlank()) return emptyList()
+        val base = backendUrl.trimEnd('/')
+        val encoded = java.net.URLEncoder.encode(artistName, "UTF-8")
+        return http.get("$base/api/events/$encoded").body()
+    }
+}

android/app/src/main/kotlin/com/novasonic/app/api/model/EventModels.kt

@@ -0,0 +1,23 @@
+package com.novasonic.app.api.model
+
+import kotlinx.serialization.Serializable
+
+@Serializable
+data class ConcertEvent(
+    val datetime: String = "",
+    val venue: ConcertVenue? = null,
+    val offers: List<ConcertOffer> = emptyList(),
+)
+
+@Serializable
+data class ConcertVenue(
+    val name: String? = null,
+    val city: String? = null,
+    val country: String? = null,
+)
+
+@Serializable
+data class ConcertOffer(
+    val url: String? = null,
+    val status: String? = null,
+)

android/app/src/main/kotlin/com/novasonic/app/ui/component/ConcertsSheet.kt

@@ -0,0 +1,169 @@
+package com.novasonic.app.ui.component
+
+import android.content.Intent
+import android.net.Uri
+import androidx.compose.foundation.background
+import androidx.compose.foundation.border
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.*
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.items
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.material3.*
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.platform.LocalContext
+import androidx.compose.ui.text.font.FontWeight
+import androidx.compose.ui.unit.dp
+import androidx.compose.ui.unit.sp
+import com.novasonic.app.api.model.ConcertEvent
+import com.novasonic.app.ui.theme.*
+import java.time.ZonedDateTime
+import java.time.format.DateTimeFormatter
+import java.util.Locale
+
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun ConcertsSheet(
+    artistName: String,
+    events: List<ConcertEvent>,
+    onDismiss: () -> Unit,
+) {
+    val context = LocalContext.current
+
+    ModalBottomSheet(
+        onDismissRequest = onDismiss,
+        containerColor   = NsSurface,
+        shape            = RoundedCornerShape(topStart = 20.dp, topEnd = 20.dp),
+    ) {
+        Text(
+            "Konzerte · $artistName",
+            fontFamily = Outfit, fontWeight = FontWeight.Bold, fontSize = 16.sp,
+            color = NsOnSurface,
+            modifier = Modifier.padding(start = 20.dp, end = 20.dp, bottom = 16.dp),
+        )
+
+        if (events.isEmpty()) {
+            Box(
+                contentAlignment = Alignment.Center,
+                modifier = Modifier
+                    .fillMaxWidth()
+                    .padding(vertical = 40.dp),
+            ) {
+                Text(
+                    "Keine Konzerte angekündigt",
+                    fontFamily = Outfit, fontSize = 14.sp,
+                    color = NsOnSurface2,
+                )
+            }
+        } else {
+            LazyColumn(
+                contentPadding = PaddingValues(start = 16.dp, end = 16.dp, bottom = 32.dp),
+                verticalArrangement = Arrangement.spacedBy(10.dp),
+            ) {
+                items(events) { event ->
+                    EventRow(event = event, onTicketClick = { url ->
+                        runCatching {
+                            context.startActivity(Intent(Intent.ACTION_VIEW, Uri.parse(url)))
+                        }
+                    })
+                }
+            }
+        }
+    }
+}
+
+@Composable
+private fun EventRow(event: ConcertEvent, onTicketClick: (String) -> Unit) {
+    val (dateStr, timeStr) = formatEventDateTime(event.datetime)
+    val venue   = event.venue?.name.orEmpty()
+    val city    = listOfNotNull(event.venue?.city, event.venue?.country).joinToString(", ")
+    val offer   = event.offers.firstOrNull { !it.url.isNullOrBlank() }
+    val soldOut = offer?.status == "unavailable"
+
+    Row(
+        verticalAlignment = Alignment.CenterVertically,
+        modifier = Modifier
+            .fillMaxWidth()
+            .clip(RoundedCornerShape(12.dp))
+            .background(NsSurface2)
+            .padding(horizontal = 14.dp, vertical = 12.dp),
+    ) {
+        // Date block
+        Column(
+            horizontalAlignment = Alignment.CenterHorizontally,
+            modifier = Modifier.width(52.dp),
+        ) {
+            Text(
+                dateStr,
+                fontFamily = Outfit, fontWeight = FontWeight.Bold,
+                fontSize = 13.sp, color = NsAccent,
+            )
+            if (timeStr.isNotBlank()) {
+                Text(
+                    timeStr,
+                    fontFamily = Outfit, fontSize = 11.sp, color = NsOnSurface2,
+                )
+            }
+        }
+
+        Spacer(Modifier.width(14.dp))
+        Box(Modifier.width(1.dp).height(36.dp).background(NsBorder))
+        Spacer(Modifier.width(14.dp))
+
+        // Venue
+        Column(Modifier.weight(1f)) {
+            if (venue.isNotBlank()) {
+                Text(
+                    venue, fontFamily = Outfit, fontWeight = FontWeight.SemiBold,
+                    fontSize = 13.sp, color = NsOnSurface,
+                    maxLines = 1,
+                )
+            }
+            if (city.isNotBlank()) {
+                Text(
+                    city, fontFamily = Outfit, fontSize = 12.sp, color = NsOnSurface2,
+                    maxLines = 1,
+                )
+            }
+        }
+
+        // Ticket button
+        if (offer?.url != null) {
+            Spacer(Modifier.width(10.dp))
+            Box(
+                contentAlignment = Alignment.Center,
+                modifier = Modifier
+                    .clip(RoundedCornerShape(8.dp))
+                    .then(
+                        if (soldOut) Modifier.border(1.dp, NsOnSurface2.copy(alpha = 0.3f), RoundedCornerShape(8.dp))
+                        else Modifier.background(NsAccent)
+                    )
+                    .clickable(enabled = !soldOut) { onTicketClick(offer.url) }
+                    .padding(horizontal = 10.dp, vertical = 6.dp),
+            ) {
+                Text(
+                    if (soldOut) "Ausverkauft" else "Tickets →",
+                    fontFamily = Outfit, fontWeight = FontWeight.SemiBold,
+                    fontSize = 11.sp,
+                    color = if (soldOut) NsOnSurface2 else Color.White,
+                )
+            }
+        }
+    }
+}
+
+private fun formatEventDateTime(datetime: String): Pair<String, String> {
+    return try {
+        val zdt = ZonedDateTime.parse(datetime)
+        val date = zdt.format(DateTimeFormatter.ofPattern("dd. MMM yyyy", Locale.GERMAN))
+        val time = if (zdt.hour == 0 && zdt.minute == 0) ""
+                   else zdt.format(DateTimeFormatter.ofPattern("HH:mm"))
+        date to time
+    } catch (_: Exception) {
+        datetime.take(10) to ""
+    }
+}

android/app/src/main/kotlin/com/novasonic/app/ui/screen/ArtistDetailScreen.kt

@@ -14,6 +14,7 @@ import androidx.compose.foundation.shape.CircleShape
 import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.automirrored.filled.ArrowBack
+import androidx.compose.material.icons.filled.Event
 import androidx.compose.material.icons.filled.PlayArrow
 import androidx.compose.material.icons.filled.Shuffle
 import androidx.compose.ui.graphics.vector.ImageVector
@@ -36,6 +37,7 @@ import coil.compose.AsyncImage
 import com.novasonic.app.api.model.Song
 import com.novasonic.app.player.PlayerState
 import com.novasonic.app.ui.component.AlbumCard
+import com.novasonic.app.ui.component.ConcertsSheet
 import com.novasonic.app.ui.component.ItunesDownloadSheet
 import com.novasonic.app.ui.component.SongRow
 import com.novasonic.app.ui.theme.*
@@ -58,6 +60,18 @@ fun ArtistDetailScreen(
     BackHandler(enabled = state.partialAlbum != null) { vm.dismissPartialAlbum() }
     BackHandler(enabled = state.subAlbumItem != null && state.partialAlbum == null) { vm.dismissSubAlbum() }
 
+    // Concerts sheet
+    if (state.showEventsSheet) {
+        val artist = state.artist
+        if (artist != null) {
+            ConcertsSheet(
+                artistName = artist.name,
+                events     = state.events,
+                onDismiss  = vm::dismissEventsSheet,
+            )
+        }
+    }
+
     // Download sheet
     state.downloadSheetItem?.let { item ->
         ItunesDownloadSheet(
@@ -195,6 +209,11 @@ fun ArtistDetailScreen(
                 ArtistActionPill(Icons.Default.Shuffle, "Shuffle") {
                     if (state.topSongs.isNotEmpty()) onPlay(state.topSongs.shuffled(), 0)
                 }
+                val eventCount = state.events.size
+                val konzertLabel = if (eventCount > 0) "Konzerte ($eventCount)" else "Konzerte"
+                ArtistActionPill(Icons.Default.Event, konzertLabel) {
+                    vm.openEventsSheet()
+                }
             }
         }
 

android/app/src/main/kotlin/com/novasonic/app/viewmodel/ArtistViewModel.kt

@@ -5,9 +5,11 @@ import android.media.MediaPlayer
 import androidx.lifecycle.AndroidViewModel
 import androidx.lifecycle.SavedStateHandle
 import androidx.lifecycle.viewModelScope
+import com.novasonic.app.api.EventsClient
 import com.novasonic.app.api.ImporterClient
 import com.novasonic.app.api.ItunesClient
 import com.novasonic.app.api.model.Artist
+import com.novasonic.app.api.model.ConcertEvent
 import com.novasonic.app.api.model.ArtistInfo
 import com.novasonic.app.api.model.DownloadRequest
 import com.novasonic.app.api.model.ItunesItem
@@ -33,6 +35,9 @@ data class ArtistUiState(
     val subAlbumTitle: String = "",
     // Partial album detail (tapped incomplete album — shows downloaded + missing tracks)
     val partialAlbum: PartialAlbumState? = null,
+    // Concerts
+    val events: List<ConcertEvent> = emptyList(),
+    val showEventsSheet: Boolean = false,
     // Preview + download
     val previewingId: Long? = null,
     val downloadSheetItem: ItunesItem? = null,
@@ -75,8 +80,13 @@ class ArtistViewModel(app: Application, savedState: SavedStateHandle) : AndroidV
                     isLoading = false, itunesLoading = true,
                 )
 
-                // Fetch iTunes data without blocking the main screen
+                // Fetch iTunes + events in parallel without blocking the main screen
                 launch { loadItunesData(artist.name) }
+                launch {
+                    val backendUrl = repo.getBackendUrl()
+                    val ev = runCatching { EventsClient.fetchEvents(backendUrl, artist.name) }.getOrDefault(emptyList())
+                    _state.value = _state.value.copy(events = ev)
+                }
             } catch (e: Exception) {
                 _state.value = ArtistUiState(isLoading = false, itunesLoading = false, error = e.message ?: e.toString())
             }
@@ -163,6 +173,9 @@ class ArtistViewModel(app: Application, savedState: SavedStateHandle) : AndroidV
 
     // ── Download sheet ───────────────────────────────────────────────────────
 
+    fun openEventsSheet()   { _state.value = _state.value.copy(showEventsSheet = true) }
+    fun dismissEventsSheet() { _state.value = _state.value.copy(showEventsSheet = false) }
+
     fun showDownloadSheet(item: ItunesItem) {
         _state.value = _state.value.copy(downloadSheetItem = item)
     }