Switch messages area to fixed positioning with centered transform for
better layout stability. Enhance scrollbar appearance with thin style,
improved colors
- Implement singleton pattern for chatApp to prevent multiple instances
- Gate initialization with isInitialized to skip repeated init calls
- Add guards for auth and WebSocket connections to avoid overlaps
- Filter non-message payloads and only render content messages
- Improve scroll-to-bottom button visibility and interaction
- Update scrollbar styling, including dark theme rules
- Added a new "Chat" link in the desktop navigation bar with appropriate click handling and active state styling.
- Updated the layout configuration to include the Chat section, mapping it to `chat/chat.html`.
- Enables users to switch to the Chat interface directly from the main navigation.
