Web UI has no responsive layout — composer/controls stack on mobile

[AYin-Z]

Describe the bug

The Web UI (served by dsh web, v0.1.0-rc.6) is not responsive on mobile viewports. On a phone browser, the components under the message composer (mode switches, permission indicator, send controls, etc.) stack/overlap into a broken layout.

Steps to reproduce

1. Start dsh web and open the UI from a mobile browser (Chrome Android / Safari iOS) at a viewport narrower than ~768px.
2. Open any session.
3. Observe the composer area: child components collapse into each other instead of wrapping/condensing.

Expected behavior

The composer and session controls adapt to narrow viewports (wrap or condense) so the UI remains usable on phones.

Analysis

The shipped CSS (index-*.css) contains no width-based media queries — the only queries are prefers-reduced-motion and pointer: coarse. The layout appears desktop-first with no mobile breakpoint handling.

Environment

• dsh version: 0.1.0-rc.6 (npm @deepseek-ai/dsh)
• Browser: Chrome mobile / Safari iOS
• OS: Android / iOS