feat: Add Chat UX improvements with notifications and @mention support

- Add ActionBar component with expandable toolbar for mobile
- Add @mention functionality with autocomplete dropdown
- Add browser notification system (push, sound, vibration)
- Add NotificationSettings modal for user preferences
- Add mention badges on room list cards
- Add ReportPreview with Markdown rendering and copy/download
- Add message copy functionality with hover actions
- Add backend mentions field to messages with Alembic migration
- Add lots field to rooms, remove templates
- Optimize WebSocket database session handling
- Various UX polish (animations, accessibility)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/modules/realtime/schemas.py

@@ -80,6 +80,7 @@ class MessageBroadcast(BaseModel):
     message_id: str
     room_id: str
     sender_id: str
+    sender_display_name: Optional[str] = None  # Display name from users table
     content: str
     message_type: MessageTypeEnum
     metadata: Optional[Dict[str, Any]] = None
@@ -141,6 +142,7 @@ class MessageResponse(BaseModel):
     message_id: str
     room_id: str
     sender_id: str
+    sender_display_name: Optional[str] = None  # Display name from users table
     content: str
     message_type: MessageTypeEnum
     metadata: Optional[Dict[str, Any]] = Field(None, alias="message_metadata")