feat: enhance Google Docs and Drive functionality

- Add insert_doc_image_from_drive() with permission checking
- Add insert_doc_image_url() for URL-based image insertion
- Add gdrive/drive_file_permissions.py with permission utilities
- Add gdrive/drive_helpers.py with Drive utility functions
- Add create_insert_text_segment_request() helper for headers/footers
- Improve error handling to distinguish auth vs validation errors
- Maintain backward compatibility with existing functionality
- Include comprehensive error messages and user guidance

Tested successfully with real Google Workspace integration.

core/utils.py

@@ -295,12 +295,16 @@ def handle_http_errors(tool_name: str, is_read_only: bool = False, service_type:
                                 f"The required API is not enabled for your project. "
                                 f"Please check the Google Cloud Console to enable it."
                             )
-                    else:
+                    elif error.resp.status in [401, 403]:
+                        # Authentication/authorization errors
                         message = (
                             f"API error in {tool_name}: {error}. "
                             f"You might need to re-authenticate for user '{user_google_email}'. "
                             f"LLM: Try 'start_google_auth' with the user's email and the appropriate service_name."
                         )
+                    else:
+                        # Other HTTP errors (400 Bad Request, etc.) - don't suggest re-auth
+                        message = f"API error in {tool_name}: {error}"
                     
                     logger.error(f"API error in {tool_name}: {error}", exc_info=True)
                     raise Exception(message) from error