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  cache+server union via a request-id-tagged search-event, so superseded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

@@ -28,7 +28,7 @@ use commands::{
     get_download_storage_stats, get_downloads, get_download_manager_stats, set_max_concurrent_downloads,
     get_smart_cache_stats, update_smart_cache_config, get_smart_cache_config, get_album_recommendations,
     get_album_affinity_status,
-    mark_download_completed, mark_download_failed, start_download,
+    mark_download_completed, mark_download_failed, start_download, enqueue_download, enqueue_video_downloads,
     pin_item, unpin_item, is_item_pinned,
     offline_get_items, offline_is_available, offline_search, pause_download, resume_download,
     player_cycle_repeat, player_get_audio_settings, player_get_queue, player_get_status,
@@ -96,6 +96,7 @@ use commands::{
     repository_create, repository_destroy, repository_get_libraries, repository_get_items,
     repository_get_item, repository_get_latest_items, repository_get_resume_items,
     repository_get_next_up_episodes, repository_get_recently_played_audio, repository_get_resume_movies,
+    repository_get_rediscover_albums,
     repository_get_genres, repository_search, repository_get_playback_info,
     repository_get_video_stream_url, repository_get_audio_stream_url,
     repository_report_playback_start, repository_report_playback_progress, repository_report_playback_stopped,
@@ -493,6 +494,8 @@ fn specta_builder() -> Builder<tauri::Wry> {
             mark_download_completed,
             mark_download_failed,
             start_download,
+            enqueue_download,
+            enqueue_video_downloads,
             get_download_manager_stats,
             set_max_concurrent_downloads,
             get_smart_cache_stats,
@@ -552,6 +555,7 @@ fn specta_builder() -> Builder<tauri::Wry> {
             repository_get_next_up_episodes,
             repository_get_recently_played_audio,
             repository_get_resume_movies,
+            repository_get_rediscover_albums,
             repository_get_genres,
             repository_search,
             repository_get_playback_info,