/talk passes the cold read: phone layout, keyboard and screen reader checked, with looks on the pull #8824

Follows #8752 (pull #8755 shipped copy, who and when, stick-to-bottom and the jump button, tool cards with Confirm and Cancel). Keep src/web/pages/talk.ts's server-drawn history and streaming, a small script, no React, and #8719's quiet rules.

Done looks like:

• [ ] At 360 px nothing scrolls sideways, and the composer stays above the keyboard. Every action is reachable by keyboard. New replies are announced to screen readers (an aria-live region).
• [ ] A byte budget test holds the page.
• [ ] Desk and phone looks, light and dark, taken signed in, are on the pull. A cold reader can start a chat in 10 seconds: the empty state offers three suggestions.

Files: src/web/pages/talk.ts, src/web/pages/talk_client.ts, test/talk-page.test.ts