Fix meeting planner detachment from events#1025

When a scheduled event is dragged and dropped to a different time or date, it becomes detached from its meeting planner. Expected behavior: changes made to the event should update the meeting planner. Current behavior: only edits made in the meeting planner update the event, not the other way around.
Issue:
Event becomes orphaned and marked in red.
User is prompted to add a new event.
Creating a new event defaults to the original date, as the meeting planner card does not update.
Acceptance Criteria:
Rescheduling an event keeps it linked to its meeting planner.
Changes sync both ways (event ↔ meeting planner).
No orphaned planners appear after rescheduling.