#2978 web: keep tool calls within the mobile viewport

Beschreibung

Fixes #2971. Applies the proposed flex sizing and tool-name ellipsis rules so long MCP tool names cannot widen the page, keeping status, duration and chevron visible.

CSS only: three changed lines. Verified in Chromium, Firefox and Playwright WebKit at 360–1280 px, including open/closed tool calls and all tool states.