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>

scripts/validate/validate_architecture.py

@@ -4663,7 +4663,7 @@ class ArchitectureValidator:
                     if imported_module == module_name:
                         continue
 
-                    # Skip suppression comments (# IMPORT-002 or # noqa: import-002)
+                    # Skip suppression comments (# IMPORT-002)
                     if "import-002" in line.lower():
                         continue