feat(android): swipe between Erkunden sub-tabs (Bibliothek ↔ Global)

Wrap the Erkunden content in a HorizontalPager so a left/right swipe switches
between the Bibliothek and Global search tabs, two-way synced with the TabRow: a
chip tap animates the pager; a settled swipe updates the selected tab (and stops
any preview, like a tap). Removes the idea from the backlog now that it's built.

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

CHANGELOG.md

@@ -453,7 +453,6 @@ Primary causes identified:
   - **New-release alerts:** periodic check for new albums/singles by followed artists (sources: iTunes lookup / MusicBrainz / Last.fm), surfaced in the existing in-app notification bell (and optionally push).
   - **Concert alerts:** reuse the existing **Ticketmaster** events integration to notify when a followed artist has nearby/upcoming shows.
   - Ties into the importer: a "download this new release" action straight from the notification.
-- **Android** — **Swipe between Erkunden sub-tabs** — a left/right swipe gesture on the Erkunden tab to switch between "Bibliothek" and "Global" search (instead of only tapping the chips). A fun, natural pager-style gesture (e.g. HorizontalPager).
 - **Android** — Playlist drag-and-drop / sort order
 - **Android** — Artist page iTunes fallback (for artists not in Navidrome)
 - **Android** — Romaji / Japanese sort support

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

@@ -3,6 +3,8 @@ package com.novasonic.app.ui.screen
 import androidx.compose.foundation.background
 import androidx.compose.foundation.clickable
 import androidx.compose.foundation.layout.*
+import androidx.compose.foundation.pager.HorizontalPager
+import androidx.compose.foundation.pager.rememberPagerState
 import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.LazyRow
 import androidx.compose.foundation.lazy.items
@@ -148,6 +150,17 @@ fun ExploreScreen(
         return
     }
 
+    // Swipe left/right to switch between the Bibliothek and Erkunden sub-tabs, kept in sync with the
+    // TabRow: a chip tap animates the pager; a settled swipe updates the selected tab.
+    val pagerState = rememberPagerState(initialPage = state.tab.ordinal) { ExploreTab.values().size }
+    LaunchedEffect(state.tab) {
+        if (pagerState.currentPage != state.tab.ordinal) pagerState.animateScrollToPage(state.tab.ordinal)
+    }
+    LaunchedEffect(pagerState.settledPage) {
+        val t = ExploreTab.values()[pagerState.settledPage]
+        if (t != state.tab) { vm.selectTab(t); vm.stopPreview() }
+    }
+
     Column(Modifier.fillMaxSize()) {
         // ── Tabs ─────────────────────────────────────────────────────────────
         TabRow(
@@ -230,26 +243,31 @@ fun ExploreScreen(
             }
         }
 
-        // ── Content ──────────────────────────────────────────────────────────
-        when (state.tab) {
-            ExploreTab.LIBRARY -> LibrarySearchContent(
-                query       = state.query,
-                coverUrl    = coverUrl,
-                playerState = playerState,
-                onSongPlay  = onSongPlay,
-                onAlbumClick = onAlbumClick,
-                onArtistClick = onArtistClick,
-                onShowContextMenu = onShowContextMenu,
-            )
-            ExploreTab.GLOBAL  -> GlobalExploreContent(
-                state        = state,
-                vm           = vm,
-                coverUrl     = coverUrl,
-                playerState  = playerState,
-                onAlbumClick = onAlbumClick,
-                onSongPlay   = onSongPlay,
-                onDownload   = vm::showDownloadSheet,
-            )
+        // ── Content (swipeable) ────────────────────────────────────────────────
+        HorizontalPager(
+            state = pagerState,
+            modifier = Modifier.weight(1f),
+        ) { page ->
+            when (page) {
+                ExploreTab.LIBRARY.ordinal -> LibrarySearchContent(
+                    query       = state.query,
+                    coverUrl    = coverUrl,
+                    playerState = playerState,
+                    onSongPlay  = onSongPlay,
+                    onAlbumClick = onAlbumClick,
+                    onArtistClick = onArtistClick,
+                    onShowContextMenu = onShowContextMenu,
+                )
+                else -> GlobalExploreContent(
+                    state        = state,
+                    vm           = vm,
+                    coverUrl     = coverUrl,
+                    playerState  = playerState,
+                    onAlbumClick = onAlbumClick,
+                    onSongPlay   = onSongPlay,
+                    onDownload   = vm::showDownloadSheet,
+                )
+            }
         }
     }
 }