feat(library): genre sliders, artist links, and navigation utils

- music landing: diverse per-genre album sliders (online counts /
  offline wide-probe fallback) and home-screen library shortcuts
- add ArtistLinks component and shared navigation/genreDiversity utils
- player/playback-mode refinements across Rust and frontend

src-tauri/android/src/main/java/com/dtourolle/jellytau/player/JellyTauPlayer.kt

@@ -138,6 +138,15 @@ class JellyTauPlayer(private val appContext: Context) {
     /** Current media ID being played */
     private var currentMediaId: String? = null
 
+    /**
+     * Guards against nativeOnPlaybackEnded() firing more than once per loaded
+     * media. ExoPlayer can re-enter STATE_ENDED (e.g. transient buffering near
+     * end of a transcoded stream), which would otherwise notify the backend
+     * twice and, for example, decrement the sleep-timer episode counter twice.
+     * Reset whenever new media is loaded.
+     */
+    private var endedNotified = false
+
     /** Current media metadata for notification updates */
     private var currentTitle: String = ""
     private var currentArtist: String = ""
@@ -208,7 +217,15 @@ class JellyTauPlayer(private val appContext: Context) {
                         // Playback completed
                         android.util.Log.d("JellyTauPlayer", "▶ Playback ended")
                         stopPositionUpdates()
-                        nativeOnPlaybackEnded()
+                        // Only notify the backend once per loaded media. ExoPlayer
+                        // can re-enter STATE_ENDED, which would double-count things
+                        // like the sleep-timer episode counter.
+                        if (!endedNotified) {
+                            endedNotified = true
+                            nativeOnPlaybackEnded()
+                        } else {
+                            android.util.Log.d("JellyTauPlayer", "▶ Playback ended already notified - ignoring")
+                        }
                     }
                     Player.STATE_BUFFERING -> {
                         android.util.Log.d("JellyTauPlayer", "▶ Buffering...")
@@ -322,6 +339,7 @@ class JellyTauPlayer(private val appContext: Context) {
     fun load(url: String, mediaId: String) {
         mainHandler.post {
             currentMediaId = mediaId
+            endedNotified = false
             val mediaItem = MediaItem.fromUri(url)
             exoPlayer.setMediaItem(mediaItem)
             exoPlayer.prepare()
@@ -552,6 +570,7 @@ class JellyTauPlayer(private val appContext: Context) {
     ) {
         mainHandler.post {
             currentMediaId = mediaId
+            endedNotified = false
 
             // Store metadata for notification updates
             currentTitle = title