Draw a peer message above the turn it started, not below it

The live Claude Code path only learns a turn was another agent's when
the turn ends -- the whole of the message arrives as an `origin` object
on the `result` -- so the note was appended after everything it caused,
and the transcript showed the answer above the question.

It cannot be recorded in place: by the time anyone knows, the reply is
already written, and the transcript is append-only. So the event carries
where it belongs instead. `PeerMessage` gains `turnStart`, the seq of
the status that opened its turn, stamped by the pump -- the only thing
that knows a seq and the only thing that sees every driver's turns. The
phone gives the note that seq, so it sorts into place rather than being
drawn out of order at the end. A status draws no row, so there is
nothing for it to collide with and the list stays sorted, which the
scroll anchor and paging both depend on.

Absent where there is nothing to correct: a message replayed out of a
session file by `import` is already in the right place, and one that
opened no turn has no turn to sit above. Both stay where they arrive.

The echo driver gets `/peer-turn` for the live shape, beside `/peer` for
the in-place one. Verified on the emulator both ways, live and on
replay, plus an ordinary `/tools` turn to confirm the run grouping the
insertion cuts through is unaffected.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

server/src/session/claude/translate.rs

@@ -1147,6 +1147,9 @@ mod tests {
                 Event::PeerMessage {
                     from: "ai-app-2-fb".to_string(),
                     text: "Reply with just the word ACK.".to_string(),
+                    // Stamped by the pump, which is the only place that
+                    // knows what seq the turn started at.
+                    turn_start: None,
                 },
                 Event::UsageDelta {
                     tokens: 7,