fix(backend/dm): include attachmentUrl + replyTo in history response

Map-response dropped attachment fields and reply reference even though
getDmHistory loads them — caused images and reply quotes to disappear
on conversation re-open.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/server/api/chat/dm/[userId].get.ts

@@ -27,10 +27,23 @@ export default defineEventHandler(async (event) => {
       : { id: partnerId, nickname: "Anonym", username: "anonym", avatar: null },
     messages: [...messages].reverse().map((m) => ({
       id: m.id,
+      senderId: m.senderId,
+      receiverId: m.receiverId,
       content: m.content,
       createdAt: m.createdAt,
       isOwn: m.senderId === user.id,
       readAt: m.readAt,
+      attachmentUrl: m.attachmentUrl,
+      attachmentType: m.attachmentType,
+      attachmentName: m.attachmentName,
+      likesCount: m.likesCount,
+      replyTo: m.replyTo
+        ? {
+            id: m.replyTo.id,
+            senderId: m.replyTo.senderId,
+            content: m.replyTo.content,
+          }
+        : null,
     })),
   };
 });