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/tests/test_models.py

@@ -1,6 +1,7 @@
 from src.core.config_models import Environment
 from src.core.logger import belief_scope
 
+
 # [DEF:test_environment_model:Function]
 # @RELATION: TESTS -> Environment
 # @PURPOSE: Tests that Environment model correctly stores values.