Phase 28 (Step 3a): /sent returns full message detail per recipient

Phase 28's in-game mail UI threads sent messages by the recipient
race name, so the bulk `/sent` endpoint now returns the same
`UserMailMessageDetail` shape as `/inbox` — single sends contribute
one row per message, broadcasts contribute one row per addressee
and the UI collapses them by `message_id` into a stand-alone item.

- `Store.ListSent` / `Service.ListSent` switched from `[]Message`
  to `[]InboxEntry`. SQL grows an INNER JOIN with
  `diplomail_recipients`.
- Handler emits `userMailMessageDetailWire` items; the deprecated
  `userMailSentSummaryWire` is removed.
- `openapi.yaml`: `UserMailSentList.items` now reference
  `UserMailMessageDetail`; the standalone `UserMailSentSummary`
  schema is dropped.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/internal/diplomail/store.go

@@ -243,25 +243,38 @@ func (s *Store) ListInbox(ctx context.Context, gameID, userID uuid.UUID) ([]Inbo
 	return out, nil
 }
 
-// ListSent returns messages authored by senderUserID in gameID,
-// newest first. Personal messages only — admin/system rows have
-// `sender_user_id IS NULL` and are filtered out by the WHERE clause.
-func (s *Store) ListSent(ctx context.Context, gameID, senderUserID uuid.UUID) ([]Message, error) {
+// ListSent returns the sender-side view of personal messages
+// authored by senderUserID in gameID, newest first. Each
+// `InboxEntry` carries the message together with one of its
+// recipient rows — single sends produce one entry per message;
+// game broadcasts produce one entry per addressee (the in-game
+// mail UI collapses broadcast entries into a single stand-alone
+// item by `message_id`). Admin / system rows have
+// `sender_user_id IS NULL` and are excluded by the WHERE clause.
+func (s *Store) ListSent(ctx context.Context, gameID, senderUserID uuid.UUID) ([]InboxEntry, error) {
 	m := table.DiplomailMessages
-	stmt := postgres.SELECT(messageColumns()).
-		FROM(m).
+	r := table.DiplomailRecipients
+	cols := append(messageColumns(), recipientColumns()...)
+	stmt := postgres.SELECT(cols).
+		FROM(m.INNER_JOIN(r, r.MessageID.EQ(m.MessageID))).
 		WHERE(
 			m.GameID.EQ(postgres.UUID(gameID)).
 				AND(m.SenderUserID.EQ(postgres.UUID(senderUserID))),
 		).
-		ORDER_BY(m.CreatedAt.DESC(), m.MessageID.DESC())
-	var rows []model.DiplomailMessages
-	if err := stmt.QueryContext(ctx, s.db, &rows); err != nil {
+		ORDER_BY(m.CreatedAt.DESC(), m.MessageID.DESC(), r.RecipientID.ASC())
+	var dest []struct {
+		model.DiplomailMessages
+		Recipient model.DiplomailRecipients `alias:"diplomail_recipients"`
+	}
+	if err := stmt.QueryContext(ctx, s.db, &dest); err != nil {
 		return nil, fmt.Errorf("diplomail store: list sent %s/%s: %w", gameID, senderUserID, err)
 	}
-	out := make([]Message, 0, len(rows))
-	for _, row := range rows {
-		out = append(out, messageFromModel(row))
+	out := make([]InboxEntry, 0, len(dest))
+	for _, row := range dest {
+		out = append(out, InboxEntry{
+			Message:   messageFromModel(row.DiplomailMessages),
+			Recipient: recipientFromModel(row.Recipient),
+		})
 	}
 	return out, nil
 }