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  cache+server union via a request-id-tagged search-event, so superseded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

@@ -91,15 +91,18 @@
         // Get target directory for downloads
         const targetDir = await commands.storageGetPath();
 
-        // Start each queued track download
+        // Enqueue each track with its resolved stream URL. The backend queue
+        // pump starts up to max_concurrent at a time and advances through the
+        // rest automatically as slots free up — so we never hit (and silently
+        // drop) the concurrency limit the way startDownload did.
         for (let i = 0; i < tracks.length && i < downloadIds.length; i++) {
           try {
             const streamUrl = await repo.getAudioStreamUrl(tracks[i].id);
             if (streamUrl) {
-              await commands.startDownload(downloadIds[i], streamUrl, targetDir);
+              await commands.enqueueDownload(downloadIds[i], streamUrl, targetDir);
             }
           } catch (e) {
-            console.error(`Failed to start download for track ${tracks[i].id}:`, e);
+            console.error(`Failed to enqueue download for track ${tracks[i].id}:`, e);
           }
         }