feat(messages): stream history one-message-per-WS-frame instead of 50-row batch

- backend: add streamMany generator (paginated, yields one record at a time)
  + messagesService.streamMessages + WS 'stream_messages' handler emitting
  'message_snapshot' per message, 'message_snapshot_end' with nextCursor
- frontend: useMessagesStream hook accumulates snapshots into SWR list,
  SSR getMessages seeds first paint, WsHook gains sendText
- add stream-many.test.ts locking the one-at-a-time + cursor contract

services/frontend/src/lib/api/server.ts

@@ -99,3 +99,26 @@ export async function getRecordings(limit = 50): Promise<PaginatedRecordings> {
     limit,
   }) as unknown as Promise<PaginatedRecordings>;
 }
+
+// ---- Messages (SSR seed for the streaming view) ----
+// Used to seed the first paint so the feed isn't blank before the WS stream
+// arrives. The client then takes over and streams the rest one frame at a time.
+export async function getMessages(
+  guildId: string,
+  channelId?: string,
+  limit = 50,
+  cursor?: string,
+): Promise<{
+  data: import("@/lib/types").MessageRecord[];
+  nextCursor: string | null;
+}> {
+  return serverOrpc().messages.list({
+    guildId,
+    channelId,
+    limit,
+    cursor,
+  }) as unknown as Promise<{
+    data: import("@/lib/types").MessageRecord[];
+    nextCursor: string | null;
+  }>;
+}