💡 RFC: Mobile & responsive viewport adaptations for Web UI (dsh web)

[mohitmathur95]

Hello,

Currently, running dsh web on smaller screens (mobile viewports or narrow windows) causes layout overlapping, particularly with the sidebar expanding over the message composer area.

A few targeted CSS/UI adjustments in @deepseek-ai/dsh-web could resolve this cleanly:

1. Collapsible drawer mode on narrow viewports: Automatically collapse the left workspace/session sidebar into a hidden slide-over drawer when the screen width drops below 768px.
2. Fixed position composer: Ensure the chat input area (composer) sticks to the bottom with env(safe-area-inset-bottom) applied so it doesn't get pushed off-screen on mobile Safari/Chrome.
3. Trajectory view touch scrolling: Add overflow-y: touch smooth scrolling to the ui-trajectory trace panel on touch devices.

thanks