feat(chat): implement pull-to-refresh functionality and pagination for chat history

src/stores/chat/chat-state.ts

@@ -33,6 +33,10 @@ export interface ChatState {
   shortfallCredits: number;
   /** history 首屏可展示标志（本地快照加载完成即可进入 ready）。 */
   historyLoaded: boolean;
+  historyTotal: number;
+  historyLimit: number;
+  nextHistoryOffset: number;
+  isLoadingMoreHistory: boolean;
   paymentUnlockPending: boolean;
   unlockHistoryPromptVisible: boolean;
   lockedHistoryCount: number;
@@ -61,6 +65,10 @@ export const initialState: ChatState = {
   requiredCredits: 0,
   shortfallCredits: 0,
   historyLoaded: false,
+  historyTotal: 0,
+  historyLimit: 50,
+  nextHistoryOffset: 0,
+  isLoadingMoreHistory: false,
   paymentUnlockPending: false,
   unlockHistoryPromptVisible: false,
   lockedHistoryCount: 0,