fix(db): await AsyncConnection.execution_options in run_maintenance

execution_options() is a coroutine on AsyncConnection and must be awaited;
the un-awaited call returned a coroutine, so exec_driver_sql() blew up with
AttributeError and every table's VACUUM was skipped (Run-now reported 0/6).
A prior change had wrongly dropped the await. Fix it and make the test mock
execution_options async so this call shape is actually exercised.

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

src/scribe/services/db_maintenance.py

@@ -66,9 +66,10 @@ async def run_maintenance(tables: tuple[str, ...] | list[str] | None = None) ->
     results: list[dict] = []
 
     async with engine.connect() as conn:
-        # execution_options() is synchronous on AsyncConnection; it returns the
-        # connection with AUTOCOMMIT set (VACUUM can't run in a transaction).
-        autocommit = conn.execution_options(isolation_level="AUTOCOMMIT")
+        # On AsyncConnection, execution_options() is a coroutine and MUST be
+        # awaited (it returns the connection with AUTOCOMMIT set — VACUUM can't
+        # run inside a transaction block).
+        autocommit = await conn.execution_options(isolation_level="AUTOCOMMIT")
         for table in targets:
             t0 = time.monotonic()
             try: