chore: round-4 polish + standardize on module-level loggers

Round-4 review (non-blocking) items:
- get_procrastinate_conninfo: warn on an empty connect_timeout= value (it falls
  back to the 10s default); preserve an explicit connect_timeout=0.
- Document the _doc_queueing_lock user_id invariant (NC rejects ':' in usernames).
- docs/configuration.md: note that `db downgrade` leaves procrastinate's tables
  in place and how to drop them on a full teardown.
- reclaim_stalled_ingest_jobs: debug heartbeat log when nothing is stalled.
- Drop the redundant list() wrap in the integration stalled-jobs assertion.

Logging pattern: define a module-level `logger = logging.getLogger(__name__)`
and use it instead of function-local or inline getLogger(__name__) calls
(config.py, config_validators.py, tests/.../test_scope_authorization.py). The
test file's dev-only `scripts.*` import gets a ty: ignore since it resolves via
sys.path at runtime, not as an installed package.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

nextcloud_mcp_server/config_validators.py

@@ -187,8 +187,6 @@ def detect_auth_mode(settings: Settings) -> AuthMode:
         ValueError: If explicit deployment_mode is unrecognised.
     """
 
-    logger = logging.getLogger(__name__)
-
     # ADR-021: explicit deployment mode wins
     if settings.deployment_mode:
         mode_str = settings.deployment_mode.lower().strip()