feat: enhance Google Calendar event update functionality

- Introduced helper functions `_is_date_only` and `_build_time_body` to streamline the construction of event start and end times for all-day and timed events.
- Refactored the `create_update_calendar_event_tool` to utilize the new helper functions, improving code readability and maintainability.
- Updated the Google Calendar sync service to ensure proper handling of calendar IDs with a default fallback to "primary".
- Modified the ApprovalCard component to simplify the construction of event update arguments, enhancing clarity and reducing redundancy.

surfsense_backend/app/services/google_calendar/kb_sync_service.py

@@ -209,8 +209,8 @@ class GoogleCalendarKBSyncService:
             )
 
             calendar_id = (document.document_metadata or {}).get(
-                "calendar_id", "primary"
-            )
+                "calendar_id"
+            ) or "primary"
             live_event = await loop.run_in_executor(
                 None,
                 lambda: (