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/create_admin.py

@@ -11,14 +11,15 @@ Docker usage:
     docker exec obsigate python backend/create_admin.py list
 """
 
-import sys
 import argparse
+import sys
 
 # Add parent directory to path for imports
 from pathlib import Path
+
 sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
 
-from backend.auth.user_store import create_user, get_all_users, delete_user
+from backend.auth.user_store import create_user, delete_user, get_all_users
 
 
 def main():