[chengyongru]

Summary

• Fix WebUI voice recording capability detection in Chrome.
• Use the browser-owned standard window.MediaRecorder constructor.
• Keep the modern navigator.mediaDevices.getUserMedia path without legacy fallbacks.
• Distinguish a missing microphone from blocked browser/system permission.
• Clear voice errors on retry and fade them out automatically after a few seconds.
• Localize the concise voice access messages across all supported locales.

Verification

• cd webui && npm run test -- src/tests/i18n.test.tsx src/tests/thread-composer.test.tsx (73 passed)
• cd webui && npm run build
• cd webui && npm run lint
• git diff --check