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/routes/library/+page.svelte

@@ -201,6 +201,20 @@
     <div>
       <div class="flex items-center justify-between mb-6">
         <h1 class="text-2xl font-bold text-white">Your Libraries</h1>
+        <div class="flex items-center gap-1">
+        <!-- Favourites cut across libraries, so they live beside the library
+             list rather than inside one. ux-flows §5C.2.
+             TRACES: UR-067 | DR-117 -->
+        <button
+          onclick={() => goto('/library/favorites')}
+          class="p-2 rounded-lg hover:bg-white/10 transition-colors text-gray-400 hover:text-white"
+          title="Favourites"
+          aria-label="Favourites"
+        >
+          <svg class="w-6 h-6" fill="none" stroke="currentColor" viewBox="0 0 24 24" stroke-width="2">
+            <path stroke-linecap="round" stroke-linejoin="round" d="M4.318 6.318a4.5 4.5 0 000 6.364L12 20.364l7.682-7.682a4.5 4.5 0 00-6.364-6.364L12 7.636l-1.318-1.318a4.5 4.5 0 00-6.364 0z" />
+          </svg>
+        </button>
         <button
           onclick={() => goto('/settings')}
           class="p-2 rounded-lg hover:bg-white/10 transition-colors text-gray-400 hover:text-white"
@@ -211,6 +225,7 @@
             <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M15 12a3 3 0 11-6 0 3 3 0 016 0z" />
           </svg>
         </button>
+        </div>
       </div>
 
       {#if $isLibraryLoading}