[FEATURE]: Desktop — make "Questions dismissed" undoable (click pill / hover undo icon)

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Summary

In the desktop app, when the agent asks a question and I dismiss it, the chat shows a static "Questions dismissed" pill (rendered in packages/session-ui/src/components/message-part.tsx:1577 when the question tool errors with "The user dismissed this question"). The question is gone — I can't bring it back or answer it without reverting the whole message.

Feature request

Make the dismissed question recoverable, e.g.:

• Clicking the "Questions dismissed" pill re-opens the question so it can be answered
• Or show a small undo icon on hover next to the pill that restores it

The question content is still in the message part, so this is purely a UI affordance.

Related

#25555 covers undoing/forking question answers; this is about re-opening a question after dismissing it, which that issue doesn't cover.