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  cache+server union via a request-id-tagged search-event, so superseded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/lib/components/library/TrackList.svelte

@@ -204,7 +204,7 @@
   <!-- Track Rows -->
   <div class="space-y-1">
     {#each tracks as track, index (track.id)}
-      <div class="w-full group hover:bg-[var(--color-surface-hover)] rounded-lg transition-colors relative {currentlyPlayingId === track.id ? 'bg-[var(--color-jellyfin)]/10 border-l-4 border-[var(--color-jellyfin)]' : ''}">
+      <div data-grid-index={index} class="w-full group hover:bg-[var(--color-surface-hover)] rounded-lg transition-colors relative {currentlyPlayingId === track.id ? 'bg-[var(--color-jellyfin)]/10 border-l-4 border-[var(--color-jellyfin)]' : ''}">
         <!-- Desktop View -->
         <button
           onclick={() => handleTrackClick(track, index)}