A /talk reply in progress survives a reload and shows on another device mid-stream #8815

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:

• [x] Reloading during a reply shows what has streamed so far and keeps streaming. Opening the same conversation on a second device shows the same.
• [x] The stream resumes from the last event the page saw (an event id), so nothing is repeated and nothing is lost.
• [x] A test streams a turn, disconnects halfway, reconnects with the last event id, and gets exactly the rest.

Files: src/http/api/conversation_talk.ts, src/crew/conversation.ts, src/web/pages/talk_client.ts, test/conversation-turn.test.ts

Reviewed pull #8833 at its head: ticked Reloading during a reply shows what has streamed so far and keeps streaming. Opening the same conversation on a second device shows the same.; The stream resumes from the last event the page saw (an event id), so nothing is repeated and nothing is lost.; A test streams a turn, disconnects halfway, reconnects with the last event id, and gets exactly the rest..