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/components/library/GenericMediaListPage.svelte

@@ -1,4 +1,4 @@
-<!-- TRACES: UR-007, UR-029, UR-030 | DR-007, DR-032, DR-033 -->
+<!-- TRACES: UR-007, UR-029, UR-030, UR-067 | DR-007, DR-032, DR-033, DR-116 -->
 <script lang="ts">
   import { onMount, onDestroy } from "svelte";
   import { listen, type UnlistenFn } from "@tauri-apps/api/event";
@@ -56,6 +56,7 @@
   let gridWrapper = $state<HTMLDivElement | null>(null);
   let searchQuery = $state("");
   let debouncedSearchQuery = $state("");
+  let favoritesOnly = $state(false);
   let sortBy = $state<string>("");
   let sortOrder = $state<"Ascending" | "Descending">("Ascending");
   let searchTimeout: ReturnType<typeof setTimeout> | null = null;
@@ -140,6 +141,9 @@
           sortOrder,
           recursive: true,
           limit: 10000,
+          // Narrows the listing in place; the backend owns what "favourite"
+          // resolves to online vs offline. TRACES: UR-067 | DR-116
+          favoritesOnly: favoritesOnly ? true : undefined,
         });
         items = excludePodcasts(result.items);
       }
@@ -154,6 +158,12 @@
     searchQuery = query;
   }
 
+  /// TRACES: UR-067 | DR-116
+  function toggleFavoritesOnly() {
+    favoritesOnly = !favoritesOnly;
+    loadItems();
+  }
+
   // Debounce search input (300ms delay) - skip initial mount to avoid duplicate load
   $effect(() => {
     const _query = searchQuery; // track for reactivity
@@ -266,6 +276,33 @@
       <SearchBar value={searchQuery} placeholder={searchPlaceholder} onInput={handleSearch} />
     </div>
 
+    <!-- Favourites filter. Session-scoped on purpose: a persisted filter that
+         hides most of a library reads as data loss on the next launch
+         (ux-flows §5C.2). Hidden while searching, which has no favourites
+         filter of its own. TRACES: UR-067 | DR-116 -->
+    {#if !debouncedSearchQuery.trim()}
+      <button
+        onclick={toggleFavoritesOnly}
+        aria-pressed={favoritesOnly}
+        class="px-3 py-2 rounded-lg text-sm font-medium flex items-center gap-2 transition-colors
+               {favoritesOnly
+                 ? 'bg-[var(--color-jellyfin)] text-white'
+                 : 'bg-[var(--color-surface)] text-gray-400 hover:text-white'}"
+        title={favoritesOnly ? "Showing favourites only" : "Show favourites only"}
+      >
+        <svg
+          class="w-4 h-4"
+          fill={favoritesOnly ? "currentColor" : "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>
+        Favourites
+      </button>
+    {/if}
+
     <!-- Sort (only show if there are sort options) -->
     {#if config.sortOptions.length > 0}
       <SortButtonGroup options={config.sortOptions} selected={sortBy} onSelect={handleSort} />