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-state.ts

@@ -2,14 +2,26 @@
  * Chat 状态机：State 形状 + 初始值
  *
  * 注：GuestChatQuota 仍位于 chat-machine.ts（属于业务常量，与上下文配对紧密）。
+ *
+ * 历史：
+ *   - `isGuest: boolean` 字段已**删**（由 chat-screen 派生自 `auth.loginStatus === "guest"`）
+ *   - `guestRemainingQuota` / `guestTotalQuota` default **改 0**：
+ *     - 游客：chat-screen 派 `ChatInit` → readInitData 调 ChatStorage → onDone 条件赋
+ *     - 非游客：**永不被赋值**（业务事实"非游客无消息限制"）—— 0 - 1 = max(0, -1) = 0 天然 no-op
+ *     - 0 同时表示"未初始化"和"已耗尽" —— UI 用 `if (isGuest && ...)` 天然过滤
  */
 import type { UiMessage } from "@/models/chat/ui-message";
 
 export interface ChatState {
   messages: UiMessage[];
   isReplyingAI: boolean;
-  isGuest: boolean;
+  /**
+   * 游客剩余配额（次/天）—— **仅**游客业务展示用
+   * - default 0 = "未初始化" / "已耗尽"（同码，靠 `isGuest` 区分）
+   * - 非游客：永不被赋值（业务事实"无消息限制"）
+   */
   guestRemainingQuota: number;
+  /** 游客总配额（仅游客展示用） */
   guestTotalQuota: number;
   quotaExceededTrigger: number;
   isLoadingMore: boolean;
@@ -20,9 +32,8 @@ export interface ChatState {
 export const initialState: ChatState = {
   messages: [],
   isReplyingAI: false,
-  isGuest: true,
-  guestRemainingQuota: 40,
-  guestTotalQuota: 50,
+  guestRemainingQuota: 0,
+  guestTotalQuota: 0,
   quotaExceededTrigger: 0,
   isLoadingMore: false,
   hasMore: true,