fix(download): stop stale aria2 GIDs from spamming errors after queue clears

- Log expected "GID not found" tellStatus probes at DEBUG, and treat a
  forgotten GID as permanent so the poll loop recovers immediately
  instead of burning 4 retries x 3s of ERROR lines per cycle
- cancel_download tolerates a forgotten GID and always pops the
  in-memory transfer so concurrent polls cannot re-register a
  cancelled download
- Restore sweep deletes aria2 state records with no resolvable target
  path instead of skipping them forever
- Clearing the download queue now also cancels in-memory tasks, removes
  live aria2 transfers and drops persisted state for the cleared ids
  (partial files on disk are preserved)

tests/services/test_download_queue_service.py

@@ -495,3 +495,29 @@ async def test_dedup_history_collapses_same_file_and_legacy_rows(tmp_path: Path)
     history = await svc.get_history()
     remaining = {item["download_id"] for item in history["items"]}
     assert remaining == {"dl-x2", "dl-y2"}
+
+
+# ---------------------------------------------------------------------------
+# clear_queue
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_clear_queue_returns_deleted_ids(tmp_path: Path) -> None:
+    """clear_queue reports the download_ids it removed so callers can tear
+    down any in-memory tracking for them."""
+    svc = _make_service(tmp_path)
+    await svc.add_to_queue(download_id="dl-1", model_id=1)
+    await svc.add_to_queue(download_id="dl-2", model_id=2)
+    await svc.add_to_queue(download_id="dl-3", model_id=3)
+    await svc.update_status("dl-3", "downloading")
+
+    cleared = await svc.clear_queue(status_filter="queued")
+    assert sorted(cleared) == ["dl-1", "dl-2"]
+
+    remaining = await svc.get_queue()
+    assert [row["download_id"] for row in remaining] == ["dl-3"]
+
+    cleared_all = await svc.clear_queue()
+    assert cleared_all == ["dl-3"]
+    assert await svc.get_queue() == []