Add React components for assignment transfer user interface:
1. AssignmentCard.tsx: Display user's current assignment with transfer button.
Shows assignment details, current status, and allows initiating transfer requests.
2. RequestTransferDialog.tsx: Modal dialog for creating transfer requests.
- Selects target assignment from assignment list
- Optionally notes required for transfer
- Submits request to AssignmentTransfers collection
- Emits AssignmentTransferRequest event
3. Transfers page (src/app/(frontend)/transfers/): Transfer request list view.
- Requests card showing pending requests with requestor, target, current
- Approval cards for assignment leaders
- Appeal cards for rejected requests
- Completed/Cancelled status display
All components use shadcn/ui primitives, proper loading states, error handling,
and provide accessible keyboard navigation.
