Moves the Zap button from the message thread header to the message composer area, adjacent to the Send button. Refactors the Zap interface creation logic into a standalone component `ZapInterface.js` to decouple it from `MessageThread.js`. Updates `Composer.js` to support an optional `onZap` handler and renders the button with an icon-only style matching the video player's accent interaction. Updates `AppShell.js` to orchestrate the Zap interface display.
- Implement mobile view state management (`list` vs `thread`) in `ProfileModalController`.
- Update `AppShell` to apply `data-dm-view` attribute for CSS toggling.
- Update `MessageThread` to render a "Back" button on mobile.
- Add CSS rules to hide/show sidebar and thread panels based on mobile view state.
- Ensure desktop layout remains split-pane.
google-labs-jules[bot]