Make the dashboard responsive on narrow screens

[raphant]

Problem

The dashboard has no narrow-screen layout for its complete top-bar control set and floating panels.
At a 390-pixel viewport, controls can extend beyond the visible right edge even when the document itself does not scroll.

Proposed change

Define compact breakpoints for the top bar, panels, control bar, and canvas overlays.
Move secondary controls into an overflow menu when space is limited.

Acceptance criteria

• All controls remain reachable at 390 by 844 pixels.
• The top bar does not clip controls or overlap the session switcher.
• Side panels fit the viewport and keep their close buttons visible.
• Touch targets meet a 44-pixel minimum where practical.
• Browser tests cover mobile portrait, mobile landscape, tablet, and 200 percent zoom.

Source

• web/components/agent-visualizer/top-bar.tsx owns the top-bar layout.
• web/lib/agent-types.ts contains fixed panel dimensions.