Fix mypy type checking errors

- Updated mypy configuration to use Python 3.9+
- Added missing type annotations to all function parameters
- Fixed type compatibility issues in variable assignments
- Resolved unreachable code and return type warnings
- All mypy checks now pass successfully

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

wikijs/exceptions.py

@@ -63,7 +63,7 @@ class PermissionError(ClientError):
 class RateLimitError(ClientError):
     """Raised when rate limit is exceeded (429)."""
 
-    def __init__(self, message: str, retry_after: Optional[int] = None, **kwargs):
+    def __init__(self, message: str, retry_after: Optional[int] = None, **kwargs: Any) -> None:
         # Remove status_code from kwargs if present to avoid duplicate argument
         kwargs.pop("status_code", None)
         super().__init__(message, status_code=429, **kwargs)