NO_REPLY is an internal agent response that should not be visible
to users. Messages with content exactly matching 'NO_REPLY' are
now hidden from the chat view.
- Replace all French UI strings with English (Connected, Thinking, Result, Send, etc.)
- Add role="log" + aria-live="polite" to chat message area
- Add role="form" + aria-label to message input area
- Add aria-label to sidebar toggle, attach file, send, and textarea
- Add role="banner" to header, role="navigation" to sidebar
- Add role="application" to app root
