feat(scrobble): time-travel navigator (year/month) + fix stats cover art

Navigator (web + android): browse Alles / Jahr / Monat with a ‹ › stepper — see
top plays for a specific month or year (e.g. March 2024). Steps into the future
are disabled. Uses the existing /scrobble/stats endpoint with computed from/to +
bucket (month for year view, day for month view). All windows verified.

Cover art fix: the app resolves covers from the Subsonic **coverArt token**, not
the raw entity id — so stats covers (which used albumId/songId) never loaded.
Now the play-log stores each play's coverArt (web + android capture), the stats
endpoint returns it for top tracks/albums, and both clients render coverUrl(coverArt)
with an id fallback. Old plays lack coverArt (blank until re-listened); artist
images still use artistId (may need getArtistInfo2 later if blank). Schema migrates
existing DBs via ALTER TABLE. SW cache -> ns-v69.

Android compileDebugKotlin + web build green; server windows + cover storage unit-tested.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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

@@ -27,6 +27,7 @@ data class StatAlbum(
     val name: String? = null,
     val albumId: String? = null,
     val artist: String? = null,
+    val coverArt: String? = null,
     val plays: Int = 0,
 )
 
@@ -37,6 +38,7 @@ data class StatTrack(
     val album: String? = null,
     val albumId: String? = null,
     val artistId: String? = null,
+    val coverArt: String? = null,
     val songId: String? = null,
     val plays: Int = 0,
 )

android/app/src/main/kotlin/com/novasonic/app/data/PlayLogClient.kt

@@ -59,6 +59,7 @@ class PlayLogClient(context: Context) {
         val artistId: String? = null,
         val album: String? = null,
         val albumId: String? = null,
+        val coverArt: String? = null,
         val duration: Int? = null,
         val playedAt: Long,
         val source: String = "android",
@@ -79,6 +80,7 @@ class PlayLogClient(context: Context) {
             artistId = song.artistId,
             album    = song.album,
             albumId  = song.albumId,
+            coverArt = song.coverArt,
             duration = song.duration,
             playedAt = System.currentTimeMillis() / 1000,
         )

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

@@ -29,9 +29,14 @@ import androidx.lifecycle.viewmodel.compose.viewModel
 import coil.compose.AsyncImage
 import com.novasonic.app.api.model.ScrobbleStats
 import com.novasonic.app.ui.theme.*
-import com.novasonic.app.viewmodel.StatsPeriod
+import com.novasonic.app.viewmodel.StatsView
 import com.novasonic.app.viewmodel.StatsViewModel
 
+private val MONTHS = listOf(
+    "Januar", "Februar", "März", "April", "Mai", "Juni",
+    "Juli", "August", "September", "Oktober", "November", "Dezember",
+)
+
 @Composable
 fun StatsScreen(
     coverUrl: (String?) -> String?,
@@ -56,24 +61,35 @@ fun StatsScreen(
             )
         }
 
-        // ── Period chips ──
+        // ── Navigator: scope chips + year/month stepper ──
         Row(
-            horizontalArrangement = Arrangement.spacedBy(8.dp),
-            modifier = Modifier.padding(start = 16.dp, top = 8.dp, bottom = 8.dp),
+            verticalAlignment = Alignment.CenterVertically,
+            modifier = Modifier.fillMaxWidth().padding(start = 16.dp, end = 12.dp, top = 8.dp, bottom = 8.dp),
         ) {
-            StatsPeriod.entries.forEach { p ->
-                val active = p == state.period
+            listOf(StatsView.ALL to "Alles", StatsView.YEAR to "Jahr", StatsView.MONTH to "Monat").forEach { (v, l) ->
+                val active = v == state.view
                 Text(
-                    p.label,
+                    l,
                     fontFamily = Outfit, fontSize = 13.sp, fontWeight = FontWeight.SemiBold,
                     color = if (active) Color.White else NsOnSurface2,
                     modifier = Modifier
+                        .padding(end = 8.dp)
                         .clip(RoundedCornerShape(999.dp))
                         .background(if (active) NsAccent else Color.Transparent)
-                        .clickable { vm.setPeriod(p) }
+                        .clickable { vm.setView(v) }
                         .padding(horizontal = 14.dp, vertical = 7.dp),
                 )
             }
+            if (state.view != StatsView.ALL) {
+                Spacer(Modifier.weight(1f))
+                StepArrow("‹", enabled = true) { vm.step(-1) }
+                Text(
+                    if (state.view == StatsView.YEAR) state.year.toString() else "${MONTHS[state.month]} ${state.year}",
+                    fontFamily = Outfit, fontSize = 14.sp, fontWeight = FontWeight.Bold, color = NsOnSurface,
+                    modifier = Modifier.padding(horizontal = 8.dp),
+                )
+                StepArrow("›", enabled = !vm.atCurrent()) { vm.step(1) }
+            }
         }
 
         when {
@@ -120,7 +136,7 @@ private fun StatsContent(d: ScrobbleStats, coverUrl: (String?) -> String?) {
         if (d.topTracks.isNotEmpty()) {
             SectionHeader("Top-Songs")
             d.topTracks.forEachIndexed { i, t ->
-                TopRow(i + 1, coverUrl(t.albumId ?: t.songId), t.title ?: "—", t.artist, t.plays)
+                TopRow(i + 1, coverUrl(t.coverArt ?: t.albumId ?: t.songId), t.title ?: "—", t.artist, t.plays)
             }
             Spacer(Modifier.height(20.dp))
         }
@@ -128,7 +144,7 @@ private fun StatsContent(d: ScrobbleStats, coverUrl: (String?) -> String?) {
         if (d.topAlbums.isNotEmpty()) {
             SectionHeader("Top-Alben")
             d.topAlbums.forEachIndexed { i, a ->
-                TopRow(i + 1, coverUrl(a.albumId), a.name ?: "—", a.artist, a.plays)
+                TopRow(i + 1, coverUrl(a.coverArt ?: a.albumId), a.name ?: "—", a.artist, a.plays)
             }
             Spacer(Modifier.height(20.dp))
         }
@@ -140,6 +156,19 @@ private fun StatsContent(d: ScrobbleStats, coverUrl: (String?) -> String?) {
     }
 }
 
+@Composable
+private fun StepArrow(glyph: String, enabled: Boolean, onClick: () -> Unit) {
+    Text(
+        glyph,
+        fontFamily = Outfit, fontSize = 20.sp, fontWeight = FontWeight.Bold,
+        color = if (enabled) NsOnSurface else NsOnSurface2.copy(alpha = 0.35f),
+        modifier = Modifier
+            .clip(RoundedCornerShape(8.dp))
+            .then(if (enabled) Modifier.clickable(onClick = onClick) else Modifier)
+            .padding(horizontal = 8.dp, vertical = 2.dp),
+    )
+}
+
 @Composable
 private fun Tile(value: String, label: String, modifier: Modifier = Modifier) {
     Column(

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

@@ -12,17 +12,15 @@ import kotlinx.coroutines.launch
 import java.util.Calendar
 import java.util.TimeZone
 
-enum class StatsPeriod(val key: String, val label: String, val bucket: String) {
-    ALL("all", "Alles", "month"),
-    YEAR("year", "Dieses Jahr", "month"),
-    LAST30("30d", "Letzte 30 Tage", "day"),
-}
+enum class StatsView { ALL, YEAR, MONTH }
 
 data class StatsUiState(
     val loading: Boolean = true,
     val configured: Boolean = true,
     val error: String? = null,
-    val period: StatsPeriod = StatsPeriod.ALL,
+    val view: StatsView = StatsView.ALL,
+    val year: Int = Calendar.getInstance().get(Calendar.YEAR),
+    val month: Int = Calendar.getInstance().get(Calendar.MONTH),   // 0-11
     val stats: ScrobbleStats? = null,
 )
 
@@ -32,37 +30,70 @@ class StatsViewModel(app: Application) : AndroidViewModel(app) {
     private val _state = MutableStateFlow(StatsUiState())
     val state: StateFlow<StatsUiState> = _state
 
-    init { load(StatsPeriod.ALL) }
+    init { load() }
 
-    fun setPeriod(p: StatsPeriod) {
-        if (p == _state.value.period && _state.value.stats != null) return
-        load(p)
+    fun setView(v: StatsView) {
+        if (v == _state.value.view) return
+        _state.value = _state.value.copy(view = v)
+        load()
     }
 
-    private fun periodRange(p: StatsPeriod): Triple<Long, Long, String> {
-        val now = System.currentTimeMillis() / 1000
-        return when (p) {
-            StatsPeriod.ALL -> Triple(0L, now + 1, p.bucket)
-            StatsPeriod.LAST30 -> Triple(now - 30L * 86400, now + 1, p.bucket)
-            StatsPeriod.YEAR -> {
-                val c = Calendar.getInstance().apply {
-                    set(Calendar.MONTH, 0); set(Calendar.DAY_OF_MONTH, 1)
-                    set(Calendar.HOUR_OF_DAY, 0); set(Calendar.MINUTE, 0); set(Calendar.SECOND, 0)
-                }
-                Triple(c.timeInMillis / 1000, now + 1, p.bucket)
+    /** Step the current year/month window by ±1 (no-op in ALL). */
+    fun step(dir: Int) {
+        val s = _state.value
+        when (s.view) {
+            StatsView.YEAR -> _state.value = s.copy(year = s.year + dir)
+            StatsView.MONTH -> {
+                var m = s.month + dir
+                var y = s.year
+                if (m < 0) { m = 11; y-- }
+                if (m > 11) { m = 0; y++ }
+                _state.value = s.copy(year = y, month = m)
             }
+            else -> return
+        }
+        load()
+    }
+
+    /** True when the shown window is the current one — used to disable stepping into the future. */
+    fun atCurrent(): Boolean {
+        val s = _state.value
+        val now = Calendar.getInstance()
+        return when (s.view) {
+            StatsView.YEAR -> s.year >= now.get(Calendar.YEAR)
+            StatsView.MONTH -> s.year > now.get(Calendar.YEAR) ||
+                (s.year == now.get(Calendar.YEAR) && s.month >= now.get(Calendar.MONTH))
+            else -> true
         }
     }
 
-    private fun load(period: StatsPeriod) {
+    private fun startOf(year: Int, month: Int, day: Int): Long {
+        val c = Calendar.getInstance().apply {
+            clear()
+            set(year, month, day, 0, 0, 0)
+        }
+        return c.timeInMillis / 1000
+    }
+
+    private fun range(): Triple<Long, Long, String> {
+        val s = _state.value
+        val nowSec = System.currentTimeMillis() / 1000
+        return when (s.view) {
+            StatsView.ALL -> Triple(0L, nowSec + 1, "month")
+            StatsView.YEAR -> Triple(startOf(s.year, 0, 1), startOf(s.year + 1, 0, 1), "month")
+            StatsView.MONTH -> Triple(startOf(s.year, s.month, 1), startOf(s.year, s.month + 1, 1), "day")
+        }
+    }
+
+    private fun load() {
         viewModelScope.launch {
-            _state.value = _state.value.copy(loading = true, error = null, period = period)
+            _state.value = _state.value.copy(loading = true, error = null)
             val settings = repo.appSettingsFlow().first()
             if (settings.scrobbleUrl.isBlank()) {
                 _state.value = _state.value.copy(loading = false, configured = false)
                 return@launch
             }
-            val (from, to, bucket) = periodRange(period)
+            val (from, to, bucket) = range()
             val tz = TimeZone.getDefault().getOffset(System.currentTimeMillis()) / 1000
             val stats = repo.fetchScrobbleStats(from, to, tz, bucket, 10)
             _state.value = if (stats == null)