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/layout.tsx

@@ -1,6 +1,6 @@
 import type { Metadata, Viewport } from "next";
 import { SessionProvider } from "@/providers/session-provider";
-import { geistSans, geistMono, athelas } from "@/lib/fonts";
+import { geistSans, geistMono, athelas } from "@/core/fonts";
 import "./globals.css";
 
 import { RootProviders } from "@/providers/root-providers";