test(ci): dispose engine between integration tests (per-loop pool)

First integration run proved the lane works (run_maintenance test passed against
real Postgres), but the health test failed with 'Future attached to a different
loop': pytest-asyncio uses a fresh loop per test while the app's module-level
engine pools a connection from the prior test's loop. Dispose the engine in each
test's teardown so the next test starts with an empty pool on its own loop.

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

tests/test_integration_db_maintenance.py

@@ -7,7 +7,9 @@ connection path that unit mocks cannot: the un-awaited
 AttributeError, reporting 0/6) passes the unit suite but fails here.
 """
 import pytest
+import pytest_asyncio
 
+from scribe.models import engine
 from scribe.services.db_maintenance import (
     MAINTENANCE_TABLES,
     get_table_health,
@@ -17,6 +19,19 @@ from scribe.services.db_maintenance import (
 pytestmark = pytest.mark.integration
 
 
+@pytest_asyncio.fixture(autouse=True)
+async def _dispose_engine():
+    """Dispose the app's module-level engine after each test.
+
+    The engine pools asyncpg connections per event loop, but pytest-asyncio runs
+    each test on a fresh loop — so without this, test 2 gets handed test 1's
+    connection bound to a now-dead loop ("Future attached to a different loop").
+    Disposing in the test's own loop teardown clears the pool cleanly.
+    """
+    yield
+    await engine.dispose()
+
+
 @pytest.mark.asyncio
 async def test_run_maintenance_vacuums_real_tables():
     summary = await run_maintenance()