Screen reader: no announcement when response is generating or complete (NVDA)

Part of umbrella accessibility issue: #69996

Problem

There is no signal accessible to a screen reader that Claude is still generating a response or has finished. Users must navigate manually to the bottom of the response area to check status, with no passive indication that work is ongoing.

Recommendation

• While generating: The elapsed time display should be wrapped in an ARIA live region set to aria-live="polite", allowing NVDA to periodically announce elapsed time without interrupting speech. The elapsed time element should also carry a heading (H3 or H4 recommended) so users can navigate directly to it.
• On completion: When generation finishes, an ARIA live region should be updated with a brief notice such as "Response complete." Using aria-live="polite" ensures the announcement queues after any current speech rather than interrupting it.

Environment

• Claude Code desktop app, Windows 11
• NVDA screen reader (latest stable)