/talk can edit and resend a message, regenerate a reply, and Retry a failed turn #8817

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] Edit on the person's last message resends it. Regenerate on the last reply asks again. A failed turn says what happened in plain words with Retry, never a raw error.
• [x] Replaced turns are kept in history, marked replaced, not deleted.
• [x] Tests for each, including a turn whose run failed showing Retry and no raw message.

Files: src/actions/talk.ts, src/core/conversations.ts, src/web/pages/talk.ts, src/web/pages/talk_client.ts, test/conversation-talk.test.ts

Reviewed pull #8844 at its head: ticked Edit on the person's last message resends it. Regenerate on the last reply asks again. A failed turn says what happened in plain words with Retry, never a raw error.; Replaced turns are kept in history, marked replaced, not deleted.; Tests for each, including a turn whose run failed showing Retry and no raw message..