feat(tracks): filter track list by ingest source

Add an optional `source` filter to `GET /api/v1/tracks` (and the
`TrackRepository.list`/`count` port + SQLAlchemy adapter). Lets clients
query, e.g., only uploaded tracks (`?source=upload`) newest-first — the
backing for the webui's persistent "Recently uploaded" view.

- test: upload then list with `?source=upload` (hit) / `?source=youtube`
  (miss)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/api/v1/tracks.py

@@ -71,6 +71,7 @@ async def list_tracks(
     artist_id: uuid.UUID | None = None,
     album_id: uuid.UUID | None = None,
     q: str | None = None,
+    source: str | None = Query(None, max_length=32),
     sort_by: str = Query("created_at", pattern="^(title|created_at|artist)$"),
     order: str = Query("desc", pattern="^(asc|desc)$"),
     limit: int = Query(50, ge=1, le=200),
@@ -80,12 +81,15 @@ async def list_tracks(
         artist_id=artist_id,
         album_id=album_id,
         q=q,
+        source=source,
         sort_by=sort_by,
         order=order,
         limit=limit,
         offset=offset,
     )
-    total = await track_repo.count(artist_id=artist_id, album_id=album_id, q=q)
+    total = await track_repo.count(
+        artist_id=artist_id, album_id=album_id, q=q, source=source
+    )
 
     artist_ids = list({t.artist_id for t in tracks})
     album_ids = list({t.album_id for t in tracks if t.album_id is not None})