feat(search): answer search from a local index; tier downloads by lifetime

Search's instant leg read only downloaded items, so with no downloads it
returned nothing and every keystroke fell through to a full Recursive=true
server query. It now reads the whole synced catalog through the same
availability CTE get_items uses, gated on the same include_catalog_browse
flag so search and browse cannot diverge. (UR-065, DR-108)

Also fixes three defects found while confirming that:

- items_fts grew by a full duplicate index every catalog pass. INSERT OR
  REPLACE fires no AFTER DELETE trigger without recursive_triggers, so the
  old index row was orphaned, and a TEXT PRIMARY KEY meant the replacement
  took a fresh rowid and inserted a second entry. Now a real upsert, with
  migration 021 rebuilding existing indexes. (DR-110)
- DELETE FROM items existed nowhere, so server-side deletions never
  propagated. Adds a post-crawl mark-and-sweep, scoped to crawled types,
  skipping downloaded items, and refusing to run after a partial crawl
  because items.parent_id cascades. (DR-110)
- The index omitted MusicArtist, Playlist and People, which search groups
  results by. Adds them plus people_fts (migration 022). (DR-111)

Re-indexing moves from a frontend startup call to a Rust background task
with a 6h TTL, so a long session no longer searches a stale catalog and a
restart no longer forces a crawl regardless of freshness. (DR-109, IR-030)

Downloads gain a lifetime tier. Eviction selected every completed row by
age with no download_source filter, so hitting the storage limit deleted
the oldest download -- typically one saved deliberately for offline -- to
make room for a precached track. It now reclaims only 'auto' rows, and
expired ones are reclaimed first, before live cache is evicted.
(DR-126, DR-127)

Downloaded video and audio-only handoffs now play from disk instead of
streaming; the video path had never consulted downloads at all. No
transcode is involved: MPV runs video=no and ExoPlayer has no surface for
an Audio item. (DR-123 in part, DR-128)

FTS queries are built as quoted phrases so apostrophes, hyphens and
slashes are data rather than operator syntax, and the item-type filter is
bound rather than interpolated.

Specs: docs/specs/catalog-index-search.md,
docs/specs/read-through-media-cache.md

Includes concurrently-developed favourites browsing and background-audio
stream-end handling; the two workstreams share offline.rs, lib.rs and
online.rs, so no subset of files builds independently.

src/lib/utils/favoritesView.ts

@@ -0,0 +1,54 @@
+// Favourites page presentation helpers — which scopes are offered as tabs, what
+// they are called, and how a tab is addressed in the URL.
+//
+// The *labels and tab order* are presentation and live here. What each scope
+// MEANS in Jellyfin item types is domain vocabulary and lives in Rust
+// (`SearchScope::item_types`); this file must never enumerate item types.
+//
+// TRACES: UR-067 | DR-117
+
+import type { SearchScope } from "$lib/api/bindings";
+
+/**
+ * Scopes offered as tabs, in display order. A subset of `SearchScope` chosen
+ * for presentation — the backend accepts more than a page needs to show.
+ */
+export const FAVORITE_SCOPES = ["all", "movies", "tv", "music"] as const;
+
+export type FavoritesScope = (typeof FAVORITE_SCOPES)[number];
+
+export const FAVORITE_SCOPE_LABELS: Record<FavoritesScope, string> = {
+  all: "All",
+  movies: "Movies",
+  tv: "Shows",
+  music: "Music",
+};
+
+/**
+ * Resolve the `?scope=` param to a tab, defaulting to All for anything
+ * missing or unrecognised (a hand-edited or stale URL must not blank the page).
+ */
+export function resolveFavoritesScope(raw: string | null | undefined): FavoritesScope {
+  if (!raw) return "all";
+  return (FAVORITE_SCOPES as readonly string[]).includes(raw) ? (raw as FavoritesScope) : "all";
+}
+
+/** URL for a tab. The default scope is omitted, keeping the base URL clean. */
+export function favoritesRouteUrl(scope: FavoritesScope): string {
+  return scope === "all" ? "/library/favorites" : `/library/favorites?scope=${scope}`;
+}
+
+/** Per-tab empty state copy (ux-flows §5C.2). */
+export function emptyStateMessage(scope: FavoritesScope): string {
+  const what: Record<FavoritesScope, string> = {
+    all: "Nothing favourited yet",
+    movies: "No favourite movies yet",
+    tv: "No favourite shows yet",
+    music: "No favourite music yet",
+  };
+  return `${what[scope]} — tap the heart on anything you like.`;
+}
+
+/** Compile-time guard that every tab is a scope the backend accepts. */
+const _scopesAreSearchScopes: readonly SearchScope[] = FAVORITE_SCOPES;
+void _scopesAreSearchScopes;