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/server/handlers_user_mail.go

@@ -194,9 +194,9 @@ func (h *UserMailHandlers) Sent() gin.HandlerFunc {
 			respondDiplomailError(c, h.logger, "user mail sent", ctx, err)
 			return
 		}
-		out := userMailSentListWire{Items: make([]userMailSentSummaryWire, 0, len(items))}
-		for _, m := range items {
-			out.Items = append(out.Items, mailMessageSummaryToWire(m))
+		out := userMailSentListWire{Items: make([]userMailMessageDetailWire, 0, len(items))}
+		for _, entry := range items {
+			out.Items = append(out.Items, mailMessageDetailToWire(entry, false))
 		}
 		c.JSON(http.StatusOK, out)
 	}
@@ -555,27 +555,18 @@ type userMailMessageDetailWire struct {
 	Translator        *string `json:"translator,omitempty"`
 }
 
-// userMailSentSummaryWire mirrors the response shape for the
-// sender-side listing. Recipient state is intentionally omitted (one
-// author may have N recipients per broadcast in later stages).
-type userMailSentSummaryWire struct {
-	MessageID      string `json:"message_id"`
-	GameID         string `json:"game_id"`
-	GameName       string `json:"game_name,omitempty"`
-	Kind           string `json:"kind"`
-	Subject        string `json:"subject,omitempty"`
-	Body           string `json:"body"`
-	BodyLang       string `json:"body_lang"`
-	BroadcastScope string `json:"broadcast_scope"`
-	CreatedAt      string `json:"created_at"`
-}
-
 type userMailInboxListWire struct {
 	Items []userMailMessageDetailWire `json:"items"`
 }
 
+// userMailSentListWire mirrors the response shape for the
+// sender-side listing. Phase 28's in-game UI threads sent messages
+// by the recipient's race name, so the wire carries the full
+// message detail (including the recipient snapshot) — single sends
+// contribute one row per message, broadcasts contribute one row per
+// addressee and the UI collapses them by `message_id`.
 type userMailSentListWire struct {
-	Items []userMailSentSummaryWire `json:"items"`
+	Items []userMailMessageDetailWire `json:"items"`
 }
 
 type userMailUnreadCountWire struct {
@@ -643,20 +634,6 @@ func mailMessageDetailToWire(entry diplomail.InboxEntry, justCreated bool) userM
 	return out
 }
 
-func mailMessageSummaryToWire(m diplomail.Message) userMailSentSummaryWire {
-	return userMailSentSummaryWire{
-		MessageID:      m.MessageID.String(),
-		GameID:         m.GameID.String(),
-		GameName:       m.GameName,
-		Kind:           m.Kind,
-		Subject:        m.Subject,
-		Body:           m.Body,
-		BodyLang:       m.BodyLang,
-		BroadcastScope: m.BroadcastScope,
-		CreatedAt:      m.CreatedAt.UTC().Format(timestampLayout),
-	}
-}
-
 // mailRecipientStateToWire renders the recipient row after a
 // mark-read or soft-delete call. The caller only needs the per-user
 // state, not the full message body again.