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/audit.py

@@ -8,11 +8,10 @@ Format: JSON lines (one JSON object per line) for easy parsing.
 """
 
 import json
-import os
 import logging
+import os
 from datetime import datetime, timezone
 from pathlib import Path
-from typing import Optional
 
 logger = logging.getLogger("obsigate.audit")
 
@@ -51,7 +50,7 @@ def log_file_save(
     vault_name: str,
     file_path: str,
     size: int,
-    ip: Optional[str] = None,
+    ip: str | None = None,
 ):
     """Log a file save (PUT) operation."""
     _write_entry({
@@ -69,7 +68,7 @@ def log_file_delete(
     username: str,
     vault_name: str,
     file_path: str,
-    ip: Optional[str] = None,
+    ip: str | None = None,
 ):
     """Log a file delete operation."""
     _write_entry({
@@ -85,7 +84,7 @@ def log_file_delete(
 def log_config_change(
     username: str,
     changes: dict,
-    ip: Optional[str] = None,
+    ip: str | None = None,
 ):
     """Log a configuration change."""
     _write_entry({
@@ -97,7 +96,7 @@ def log_config_change(
     })
 
 
-def log_vault_add(username: str, vault_name: str, vault_path: str, ip: Optional[str] = None):
+def log_vault_add(username: str, vault_name: str, vault_path: str, ip: str | None = None):
     """Log a vault addition."""
     _write_entry({
         "timestamp": datetime.now(timezone.utc).isoformat(),
@@ -109,7 +108,7 @@ def log_vault_add(username: str, vault_name: str, vault_path: str, ip: Optional[
     })
 
 
-def log_vault_remove(username: str, vault_name: str, ip: Optional[str] = None):
+def log_vault_remove(username: str, vault_name: str, ip: str | None = None):
     """Log a vault removal."""
     _write_entry({
         "timestamp": datetime.now(timezone.utc).isoformat(),
@@ -120,7 +119,7 @@ def log_vault_remove(username: str, vault_name: str, ip: Optional[str] = None):
     })
 
 
-def get_recent_entries(limit: int = 100, action: Optional[str] = None) -> list:
+def get_recent_entries(limit: int = 100, action: str | None = None) -> list:
     """Read the most recent audit log entries.
 
     Args: