refactor(chat): decouple chat state from auth and gate quota alerts to guests

- Remove ChatAuthStatusChanged dispatch from auth login flow; chat screen now subscribes directly to auth state machine (loginStatus) to derive isGuest and drive WS lifecycle
- Gate quota-exceeded and warning dialogs to guests only (non-guests have no message limit)
- Dispatch ChatLoadMoreHistory for non-guest initial load vs ChatInit for guests
- Fix AppConstants import path from @/core/constants/app_constants to @/core/app_constants
- Add defensive isGuest checks in quota effects to prevent non-guest quota triggers

src/stores/chat/chat-context.tsx

@@ -8,8 +8,8 @@
  * 兼容性：保持原 `useChatState()` / `useChatDispatch()` API。
  * 内部将 XState 状态机快照映射回原 `ChatState` 形状。
  *
- * 注：WebSocket 长生命周期 actor 暂未集成到状态机（保留在 chat-side-effects.ts
- * 由外部 chat-side-effects 模块管理），待下一轮迁移。
+ * 注：WebSocket 长生命周期 actor **由 chat-screen.tsx 监听 auth 状态机驱动**——
+ * 鉴权解耦（loginStatus 在 auth，chat 机器**不**感知鉴权）。
  */
 import {
   type Dispatch,
@@ -24,13 +24,17 @@ import { chatMachine } from "./chat-machine";
 import type { ChatEvent, ChatState as MachineContext } from "./chat-machine";
 
 /**
- * 对外暴露的 State 形状（保持与原 ChatState 兼容）
+ * 对外暴露的 State 形状
+ *
+ * **isGuest 字段已删** —— 由 chat-screen 派生自 `auth.loginStatus === "guest"`。
+ *   消费方（chat-screen）通过 `useAuthState()` 取 loginStatus，本地派生 isGuest。
  */
 interface ChatState {
   messages: MachineContext["messages"];
   isReplyingAI: boolean;
-  isGuest: boolean;
+  /** 游客剩余配额（次/天）—— 业务展示用，鉴权判断由 chat-screen 派生 loginStatus */
   guestRemainingQuota: number;
+  /** 游客总配额 */
   guestTotalQuota: number;
   quotaExceededTrigger: number;
   isLoadingMore: boolean;
@@ -53,7 +57,6 @@ export function ChatProvider({ children }: ChatProviderProps) {
     () => ({
       messages: state.context.messages,
       isReplyingAI: state.context.isReplyingAI,
-      isGuest: state.context.isGuest,
       guestRemainingQuota: state.context.guestRemainingQuota,
       guestTotalQuota: state.context.guestTotalQuota,
       quotaExceededTrigger: state.context.quotaExceededTrigger,