`sqlite3.Connection.__exit__` only commits/rolls back a transaction — it
does not close the connection. Python 3.13 (the Nix env on the KVM
runner) emits `ResourceWarning: unclosed database` for every connection
GC'd without an explicit close, producing noisy output in the coverage job.
Add `DbStore._connection()`, a `contextmanager` that calls `self._connect()`,
wraps it in the existing transaction context manager, and closes the
connection in a `finally` block. Change all `with self._connect() as conn:`
call sites in `db_store.py`, `audit_store.py`, `queue_store.py`, and
`orchestrator/registry.py` to `with self._connection() as conn:`.
`_connect()` remains as the per-subclass hook (RegistryStore overrides
it to set `busy_timeout`); `_connection()` delegates to `self._connect()` so
the override is respected.
didericis-claude
e33cccfdde