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/endpoints/pages.py

@@ -411,7 +411,7 @@ class PagesEndpoint(BaseEndpoint):
         """
 
         # Build variables (only include non-None values)
-        variables = {"id": page_id}
+        variables: Dict[str, Any] = {"id": page_id}
 
         if page_data.title is not None:
             variables["title"] = page_data.title