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  cache+server union via a request-id-tagged search-event, so superseded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/stores/music.ts

@@ -0,0 +1,134 @@
+// Music library landing page data store.
+// Powers the focused music landing: hero + horizontal sliders.
+// TRACES: UR-007, UR-034 | DR-007, DR-038, DR-039
+import { writable, derived } from "svelte/store";
+import type { MediaItem } from "$lib/api/types";
+import { auth } from "./auth";
+import { excludePodcasts } from "$lib/utils/podcastFilter";
+
+interface MusicState {
+  // Albums grouped from recently played tracks (backend handles grouping).
+  recentlyPlayed: MediaItem[];
+  // Most recently added albums in the music library.
+  newlyAdded: MediaItem[];
+  // User playlists.
+  playlists: MediaItem[];
+  // Albums the user has played but hasn't returned to in a while.
+  rediscover: MediaItem[];
+  // Mix of recently played + rediscover, used for the hero banner.
+  heroItems: MediaItem[];
+  isLoading: boolean;
+  error: string | null;
+}
+
+const SECTION_LIMIT = 16;
+
+function createMusicStore() {
+  const initialState: MusicState = {
+    recentlyPlayed: [],
+    newlyAdded: [],
+    playlists: [],
+    rediscover: [],
+    heroItems: [],
+    isLoading: false,
+    error: null,
+  };
+
+  const { subscribe, set, update } = writable<MusicState>(initialState);
+
+  /**
+   * Build the hero rotation from a mix of recently played and rediscover
+   * albums, interleaved so the banner alternates "fresh in your ears" with
+   * "remember this?". De-duplicates by id and prefers items that have artwork.
+   */
+  function buildHero(recent: MediaItem[], rediscover: MediaItem[]): MediaItem[] {
+    const hasArt = (i: MediaItem) =>
+      !!i.primaryImageTag || !!(i.backdropImageTags && i.backdropImageTags.length > 0);
+
+    const recentPool = recent.filter(hasArt);
+    const rediscoverPool = rediscover.filter(hasArt);
+
+    const result: MediaItem[] = [];
+    const seen = new Set<string>();
+    const maxLen = Math.max(recentPool.length, rediscoverPool.length);
+
+    for (let i = 0; i < maxLen && result.length < 6; i++) {
+      for (const candidate of [recentPool[i], rediscoverPool[i]]) {
+        if (candidate && !seen.has(candidate.id)) {
+          seen.add(candidate.id);
+          result.push(candidate);
+        }
+      }
+    }
+
+    return result.slice(0, 6);
+  }
+
+  async function loadSections(libraryId: string) {
+    update(s => ({
+      ...s,
+      isLoading: s.recentlyPlayed.length === 0 && s.newlyAdded.length === 0,
+      error: null,
+    }));
+
+    try {
+      const repo = auth.getRepository();
+
+      const [recentlyPlayed, newlyAdded, playlistsResult, rediscover] = await Promise.all([
+        repo.getRecentlyPlayedAudio(SECTION_LIMIT),
+        repo.getItems(libraryId, {
+          includeItemTypes: ["MusicAlbum"],
+          sortBy: "DateCreated",
+          sortOrder: "Descending",
+          recursive: true,
+          limit: SECTION_LIMIT,
+        }),
+        repo.getItems(libraryId, {
+          includeItemTypes: ["Playlist"],
+          sortBy: "SortName",
+          sortOrder: "Ascending",
+          recursive: true,
+          limit: SECTION_LIMIT,
+        }),
+        repo.getRediscoverAlbums(libraryId, SECTION_LIMIT),
+      ]);
+
+      // HACK: drop the "Podcasts" folder that lives inside the music library.
+      const recentlyPlayedAlbums = excludePodcasts(recentlyPlayed);
+      const newlyAddedAlbums = excludePodcasts(newlyAdded.items);
+      const playlistItems = excludePodcasts(playlistsResult.items);
+      const rediscoverAlbums = excludePodcasts(rediscover);
+
+      const heroItems = buildHero(recentlyPlayedAlbums, rediscoverAlbums);
+
+      update(s => ({
+        ...s,
+        recentlyPlayed: recentlyPlayedAlbums,
+        newlyAdded: newlyAddedAlbums,
+        playlists: playlistItems,
+        rediscover: rediscoverAlbums,
+        heroItems,
+        isLoading: false,
+      }));
+    } catch (error) {
+      const message = error instanceof Error ? error.message : "Failed to load music sections";
+      update(s => ({ ...s, isLoading: false, error: message }));
+      console.error("Failed to load music sections:", error);
+    }
+  }
+
+  function reset() {
+    set(initialState);
+  }
+
+  return {
+    subscribe,
+    loadSections,
+    reset,
+  };
+}
+
+export const music = createMusicStore();
+
+export const musicHeroItems = derived(music, $m => $m.heroItems);
+export const isMusicLoading = derived(music, $m => $m.isLoading);