Add notification mute functionality for conversations with the following changes:
- Add notification_muted field to ConversationResponse and related DTOs
- Add notificationMutedMap to message store for tracking mute state
- Add setConversationNotificationMuted API method
- Integrate mute toggle in GroupInfoScreen and PrivateChatInfoScreen
- Skip system notifications for muted conversations
- Suppress vibration for muted conversations in WS handler
- Clean up selected mentions when @mentions are removed from text
Chore changes:
- Update PostCard bookmark icon from 'bookmark' to 'star'
- Refine card styles across AppsScreen, MaterialsScreen, and SubjectMaterialsScreen
- Improve week selector scrolling to center selected week in ScheduleScreen
