chore: mypy fixes for routes.py + legal_document_service + control_export_service

- Add [mypy-compliance.api.routes] to mypy.ini strict scope
- Fix bare `dict` type annotation in routes.py update_requirement handler
- Fix Column[str] return type in control_export_service.download_file
- Fix unused type:ignore in legal_document_service.upload_word
- Add union-attr ignore for optional requirement null access in routes.py

mypy compliance/ -> Success on 149 source files
173/173 pytest pass

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend-compliance/compliance/services/control_export_service.py

@@ -317,7 +317,7 @@ class ControlExportService:
         if not export.file_path or not os.path.exists(export.file_path):
             raise NotFoundError("Export file not found")
 
-        return export.file_path
+        return str(export.file_path)
 
     def list_exports(
         self, limit: int, offset: int