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/models.py

@@ -35,9 +35,12 @@ class Message(Base):
     content = Column(Text, nullable=False)
     message_type = Column(Enum(MessageType), default=MessageType.TEXT, nullable=False)
 
-    # Message metadata for structured data, mentions, file references, etc.
+    # Message metadata for structured data, file references, etc.
     message_metadata = Column(JSON)
 
+    # @Mention tracking - stores array of mentioned user_ids
+    mentions = Column(JSON, default=list)
+
     # Timestamps
     created_at = Column(DateTime, default=datetime.utcnow, nullable=False)
     edited_at = Column(DateTime)  # Last edit timestamp