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>

pyproject.toml

@@ -94,7 +94,7 @@ known_first_party = ["wikijs"]
 known_third_party = ["pytest", "requests", "pydantic"]
 
 [tool.mypy]
-python_version = "3.8"
+python_version = "3.9"
 warn_return_any = true
 warn_unused_configs = true
 disallow_untyped_defs = true