fix: message detail shows only its own images, not everyone's

useMessageDetail fetch attachments per-channel -> detail view nampilin
10 image terbaru di channel itu (semua orang), bukan image pesan yang
diklik. Root cause: getAttachmentsByChannel cuma filter channel_id.

- backend: messageQuerySchema + messageId optional; repository
  tambah eq(message_id) pas messageId ada. Sudah ada index
  idx_attachments_message.
- frontend: getAttachments(channelId, limit, cursor, messageId);
  useMessageDetail pass id pesan.

Verifikasi: backend tsc PASS, frontend tsc PASS + next build PASS.
E2E local (tsx + env prod, port 3901): tanpa messageId -> 3 row
(termasuk image.png punya message lain); dengan messageId -> tepat
2 row milik pesan itu. psql juga konfirmasi channel-only 3 vs
message-filtered 2.

services/frontend/src/hooks/use-messages.ts

@@ -136,7 +136,9 @@ export function useMessageDetail(id: string | null) {
       // can race the detail load and see detail.data === undefined.
       const cid = detail.data?.channel_id;
       if (!cid) return [];
-      const res = await messagesApi.getAttachments(cid, 10);
+      // messageId filter: attachment list must show only this message's
+      // images, not the latest images from everyone in the channel.
+      const res = await messagesApi.getAttachments(cid, 10, undefined, id ?? "");
       return res.data;
     },
   );