test(ci): add Postgres integration lane + real run_maintenance guard

The unit suite can't catch sync/async API mismatches against SQLAlchemy (an
un-awaited execution_options passed green CI but failed at runtime: VACUUM 0/6).
Add a real-Postgres integration lane modelled on the family pattern (rules
6/79-82): a new CI 'integration' job with a postgres:16 service, bridge-IP
discovery, busybox-safe readiness wait, and 'alembic upgrade head', running
pytest -m integration. Non-gating, like the unit lane.

- tests/test_integration_db_maintenance.py: runs run_maintenance() and
  get_table_health() against real Postgres; asserts all allowlisted tables
  vacuum OK (the await regression makes this fail) and health reports real stats.
- pyproject: register the 'integration' marker.
- conftest: integration-marked tests use the real DATABASE_URL, not the stub.
- ci.yml: unit 'test' job now runs -m 'not integration'.

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

pyproject.toml

@@ -36,6 +36,9 @@ where = ["src"]
 [tool.pytest.ini_options]
 asyncio_mode = "auto"
 testpaths = ["tests"]
+markers = [
+    "integration: requires a real Postgres database (runs only in the CI integration lane)",
+]
 
 [tool.ruff]
 line-length = 120