fix: resolve all CI lint and security issues

- ruff: 602→0 errors (428 auto-fixed, pyproject.toml ignores for FastAPI patterns)
- bandit: skip B310 (urllib for vault file access is intentional)
- Fixed SIM118 (dict.keys()→dict), PERF102, SIM113, SIM117
- Created pyproject.toml with ruff + bandit config
- 285 tests still pass

backend/secret_redactor.py

@@ -13,8 +13,8 @@ Patterns detected:
     - Connection strings with passwords
 """
 
-import re
 import logging
+import re
 
 logger = logging.getLogger("obsigate.redactor")