fix: test DB isolation, Discord recovery, and over-mocked tests

Test data was bleeding into production tasks.db because
swarm.task_queue.models.DB_PATH (relative path) was never patched in
conftest.clean_database. Fixed by switching to absolute paths via
settings.repo_root and adding the missing module to the patching list.

Discord bot could leak orphaned clients on retry after ERROR state.
Added _cleanup_stale() to close stale client/task before each start()
attempt, with improved logging in the token watcher.

Rewrote test_paperclip_client.py to use httpx.MockTransport instead of
patching _get/_post/_delete — tests now exercise real HTTP status codes,
error handling, and JSON parsing. Added end-to-end test for
capture_error → create_task DB isolation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/swarm/task_queue/models.py

@@ -13,7 +13,14 @@ from pathlib import Path
 
 logger = logging.getLogger(__name__)
 
-DB_PATH = Path("data/tasks.db")
+# Use absolute path via settings.repo_root so tests can reliably redirect it
+# and relative-path CWD differences don't cause DB leaks.
+try:
+    from config import settings as _settings
+
+    DB_PATH = Path(_settings.repo_root) / "data" / "tasks.db"
+except Exception:
+    DB_PATH = Path("data/tasks.db")
 
 
 @dataclass