Ease live Chat arrivals and keep the transcript anchored

New messages, Planner rows, notices, and research offer cards fade and rise
4px as they arrive, via @starting-style, while history and reconnects stay
still. Offer cards that move below a newer message slide there instead of
teleporting, the speaker's header no longer repeats after a card, and the
transcript stays on its newest line as rows grow, the pane resizes, or you
send a message. Research notices use the sparkle and warning icons, and a
ready request linked from a visible offer card announces itself only there.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>