fix(lint): pin ruff version, add pre-commit hook, fix all lint errors

- Pin ruff==0.8.4 in requirements-dev.txt (was >=0.8.4, CI got newer
  version with different import sorting rules)
- Add ruff to .pre-commit-config.yaml with --fix to auto-sort imports
  on commit (prevents PyCharm import reordering from reaching CI)
- Fix I001 import sorting in 6 files
- Fix F401 unused import (sqlalchemy.Numeric in subscription.py)
- Fix noqa false positive in validate_architecture.py comment

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/modules/monitoring/models/__init__.py

@@ -5,10 +5,9 @@ Monitoring module database models.
 Provides monitoring-related models including capacity snapshots.
 """
 
-from app.modules.monitoring.models.capacity_snapshot import CapacitySnapshot
-
 # Admin notification and logging models
 from app.modules.messaging.models import AdminNotification
+from app.modules.monitoring.models.capacity_snapshot import CapacitySnapshot
 from app.modules.tenancy.models import PlatformAlert
 
 __all__ = [