chore(lint): apply ruff --fix (4443 auto-fixes)

Auto-fixed categories:
- F401: unused imports removed
- I001: import blocks sorted
- W293: trailing whitespace stripped
- UP035: deprecated typing imports replaced
- SIM: simplify suggestions applied
- ARG: unused args prefixed with underscore
- T201: print statements removed
- F841: unused variables removed
- RUF059: unpacked variables prefixed

Remaining ~1500 unfixable errors (C901, B904, N806, E402) require manual work.

Backend smoke tests: 13/13 passed.

backend/src/core/encryption_key.py

@@ -15,7 +15,7 @@ from pathlib import Path
 
 from cryptography.fernet import Fernet
 
-from .logger import logger, belief_scope
+from .logger import belief_scope, logger
 
 DEFAULT_ENV_FILE_PATH = Path(__file__).resolve().parents[2] / ".env"