Address review: visible sheet close, origin-aware entrance, shared display name

- The phone draft sheet shows its close beside the grabber and drops the
  empty header row.
- commentCardPoint reports the card's side; the card fades in with a small
  translate from its passage.
- displayName lives in @chopin/editor and Chat uses it.
- Enter never sends while composing with an IME, and on a coarse pointer
  Enter is a newline so the send button sends.
- The marker lane defaults to 56px, matching the layer.

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