feat: enforce single invocation for tool actions across various services

- Added a guideline to ensure that each tool (Gmail, Google Calendar, Google Drive, Linear, Notion) is called only once per user request.
- Updated documentation to clarify that the system will automatically select the most relevant match when multiple items share the same title or subject, enhancing user experience and preventing redundant calls.

surfsense_backend/app/services/gmail/tool_metadata_service.py

@@ -436,6 +436,8 @@ class GmailToolMetadataService:
                     ),
                 )
             )
+            .order_by(Document.updated_at.desc().nullslast())
+            .limit(1)
         )
         row = result.first()
         if row: