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>

tests/test_upload_stream_api.py

@@ -190,3 +190,25 @@ async def test_upload_requires_auth(api: AsyncClient) -> None:
         files={"file": ("x.mp3", b"data", "audio/mpeg")},
     )
     assert resp.status_code == 401
+
+
+async def test_list_tracks_filters_by_source(api: AsyncClient) -> None:
+    # Uploaded tracks carry source="upload"; `?source=` narrows the list (this
+    # powers the webui's "Recently uploaded" view, which survives a refresh).
+    token = await _login(api)
+    headers = {"Authorization": f"Bearer {token}"}
+    await api.post(
+        "/api/v1/upload",
+        files={"file": ("uploaded.mp3", b"upload bytes" * 80, "audio/mpeg")},
+        headers=headers,
+    )
+
+    hit = await api.get("/api/v1/tracks", params={"source": "upload"}, headers=headers)
+    assert hit.status_code == 200, hit.text
+    items = hit.json()["items"]
+    assert len(items) == 1
+    assert items[0]["source"] == "upload"
+
+    miss = await api.get("/api/v1/tracks", params={"source": "youtube"}, headers=headers)
+    assert miss.status_code == 200
+    assert miss.json()["items"] == []