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  cache+server union via a request-id-tagged search-event, so superseded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/storage/schema.rs

@@ -21,6 +21,7 @@ pub const MIGRATIONS: &[(&str, &str)] = &[
     ("014_series_audio_preferences", MIGRATION_014),
     ("015_device_id", MIGRATION_015),
     ("016_autoplay_max_episodes", MIGRATION_016),
+    ("017_downloads_resume_url", MIGRATION_017),
 ];
 
 /// Initial schema migration
@@ -667,3 +668,15 @@ const MIGRATION_016: &str = r#"
 ALTER TABLE user_player_settings
 ADD COLUMN autoplay_max_episodes INTEGER DEFAULT 0;
 "#;
+
+/// Migration to persist the resolved stream URL and target directory on each
+/// download row. This lets the backend queue pump start a pending download by
+/// itself (replaying the stored URL) once a concurrency slot frees up, instead
+/// of relying on the frontend to re-issue every queued item.
+const MIGRATION_017: &str = r#"
+-- Resolved download source URL and on-disk target directory, captured when the
+-- download is enqueued. Nullable: pre-existing rows and rows enqueued without a
+-- URL simply won't be auto-started by the pump.
+ALTER TABLE downloads ADD COLUMN stream_url TEXT;
+ALTER TABLE downloads ADD COLUMN target_dir TEXT;
+"#;