Add handling for tombstoned room

[sukso96100]

Hello, Thanks for this cool matrix client :)

I got many tombstoned room (mostly due to room upgrades on other homeserver) and wanted feature for #482
So I have added some features for that.

1. Room tombstoned timeline event: This handles room tombstoned timeline event then show message "This room has been replaced" in chat timeline.

• commet/lib/client/timeline_events/timeline_event_room_tombstone.dart for defining the event type - and its implementation commet/lib/client/matrix/timeline_events/matrix_timeline_event_room_tombstone.dart
• commet/lib/ui/molecules/timeline_events/timeline_view_entry.dart for handling the new event.
• commet/lib/client/matrix/timeline_events/matrix_timeline_event_room_tombstone.dart for showing the room tombstoned timeline message

2. Room tombstoned message and Enter new room button on chat input area (Uses room state): Based on matrix room state, if the room is tombstoned, it shows "This room has been replaced" message on chat input area along with "Enter new room" button which basically resolve then joins user to the new room then make your leave the old room.

• commet/lib/client/matrix/matrix_room.dart for handling the room tombstoned state
• commet/lib/client/room.dart for access to relevant state and commet/lib/client/matrix_background/matrix_background_room.dart for access

Test demo

2026-02-25.01-10-12.mp4