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-tauri/src/commands/storage/people.rs

@@ -47,10 +47,25 @@ pub async fn storage_save_person(
     };
 
     let query = Query::with_params(
-        "INSERT OR REPLACE INTO people (
+        // A real UPSERT, not INSERT OR REPLACE — `people` is now backed by the
+        // `people_fts` index (migration 022), and REPLACE would orphan an index
+        // entry on every re-cache: it fires no AFTER DELETE trigger without
+        // `recursive_triggers`, and reassigns the rowid that `content_rowid`
+        // refers to. Same defect as DR-110 fixed for `items`.
+        //
+        // TRACES: UR-065 | DR-110, DR-111
+        "INSERT INTO people (
             id, server_id, name, overview, primary_image_tag,
             premiere_date, end_date, synced_at
-        ) VALUES (?, ?, ?, ?, ?, ?, ?, CURRENT_TIMESTAMP)",
+        ) VALUES (?, ?, ?, ?, ?, ?, ?, CURRENT_TIMESTAMP)
+        ON CONFLICT(id) DO UPDATE SET
+            server_id = excluded.server_id,
+            name = excluded.name,
+            overview = excluded.overview,
+            primary_image_tag = excluded.primary_image_tag,
+            premiere_date = excluded.premiere_date,
+            end_date = excluded.end_date,
+            synced_at = CURRENT_TIMESTAMP",
         vec![
             QueryParam::String(person.id),
             QueryParam::String(person.server_id),