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/app/sidebar/components/sidebar-screen.tsx

@@ -8,7 +8,6 @@ import { MobileShell } from "@/app/_components/core/mobile-shell";
 import { SettingsSection } from "@/app/_components/core/settings-section";
 import { useUserDispatch, useUserState } from "@/stores/user/user-context";
 import { useAuthDispatch } from "@/stores/auth/auth-context";
-import { useChatDispatch } from "@/stores/chat/chat-context";
 import { ROUTES } from "@/router/routes";
 
 import type { UserView } from "@/models/user/user";
@@ -23,7 +22,6 @@ import styles from "./sidebar-screen.module.css";
 export function SidebarScreen() {
   const user = useUserState();
   const userDispatch = useUserDispatch();
-  const chatDispatch = useChatDispatch();
   const authDispatch = useAuthDispatch();
   const router = useRouter();
 
@@ -34,17 +32,18 @@ export function SidebarScreen() {
 
   // 等价 Dart: BlocConsumer<UserBloc> 的 listener（profile_view.dart:24-34）
   // 仅在 currentUser 由非 null 跳到 null 时触发清理
+  // 注：chat 机器**不**再需要 `ChatAuthStatusChanged` 通知（已**删**）—— chat-screen
+  //     通过 `useAuthState()` 主动订阅 loginStatus；这里只需重置 auth + 跳 /chat
   const prevUserRef = useRef<UserView | null>(user.currentUser);
   useEffect(() => {
     const wasLoggedIn = prevUserRef.current != null;
     const isNowLoggedOut = user.currentUser == null;
     prevUserRef.current = user.currentUser;
     if (wasLoggedIn && isNowLoggedOut) {
-      chatDispatch({ type: "ChatAuthStatusChanged" });
       authDispatch({ type: "AuthReset" });
       router.replace(ROUTES.chat);
     }
-  }, [user.currentUser, chatDispatch, authDispatch, router]);
+  }, [user.currentUser, authDispatch, router]);
 
   return (
     <MobileShell>