feat(library): focused music/TV/movie landing screens + self-draining download queue

Library screens:
- Add dedicated music, TV, and movie landing pages (hero banner +
  horizontal carousels) backed by new music/tv/movies stores.
- Route tvshows libraries to /library/tv; surface rediscover ("haven't
  listened to in a while") albums via a new repository method across
  online/offline/hybrid repos plus the repository_get_rediscover_albums
  command.
- Add an A-Z jump bar for long alphabetically-sorted lists, with grid
  index anchors in LibraryGrid/LibraryListView/TrackList.
- Filter the "Podcasts" folder out of music library queries.

Downloads:
- Add a backend queue pump: enqueue_download / enqueue_video_downloads
  persist the resolved stream URL + target dir on each row (migration
  017), and the pump starts up to max_concurrent and drains the rest
  automatically as slots free, instead of the frontend silently dropping
  items past the concurrency limit. Album/series/season buttons now
  enqueue rather than calling start_download directly.

Other fixes:
- Hybrid search now returns instant cache results and pushes the merged
  cache+server union via a request-id-tagged search-event, so superseded
  queries can't clobber fresher results.
- URL-encode SearchTerm / genres / item types in online repo requests.
- Android: pause on audio-becoming-noisy (headphone/BT disconnect).

src-tauri/src/repository/mod.rs

@@ -79,6 +79,15 @@ pub trait MediaRepository: Send + Sync {
         limit: Option<usize>,
     ) -> Result<Vec<MediaItem>, RepoError>;
 
+    /// Get albums the user has played, but not recently ("rediscover" / haven't
+    /// listened to in a while). Returns albums sorted by least-recently played
+    /// first, optionally restricted to a parent library.
+    async fn get_rediscover_albums(
+        &self,
+        parent_id: Option<&str>,
+        limit: Option<usize>,
+    ) -> Result<Vec<MediaItem>, RepoError>;
+
     /// Get resume movies
     async fn get_resume_movies(&self, limit: Option<usize>) -> Result<Vec<MediaItem>, RepoError>;