feat(data): add paywall payment APIs

src/data/dto/chat/chat_message.ts

@@ -12,6 +12,9 @@ export class ChatMessage {
   declare readonly content: string;
   declare readonly id: string;
   declare readonly createdAt: string;
+  declare readonly isPrivate: boolean | null;
+  declare readonly privateLocked: boolean | null;
+  declare readonly privateHint: string | null;
 
   private constructor(input: ChatMessageInput) {
     const data = ChatMessageSchema.parse(input);