refactor(chat): clean stale mocks and external browser helpers

src/app/chat/chat-screen.tsx

@@ -7,6 +7,11 @@ import { useRouter } from "next/navigation";
 import { useAuthState } from "@/stores/auth/auth-context";
 import { useChatDispatch, useChatState } from "@/stores/chat/chat-context";
 import { useUserState } from "@/stores/user/user-context";
+import {
+  openChatInExternalBrowser,
+  recordExternalBrowserPromptShown,
+  resolveExternalBrowserPromptEligibility,
+} from "@/lib/chat/chat_external_browser";
 
 import { MobileShell } from "@/app/_components/core";
 
@@ -25,9 +30,6 @@ import {
   getChatPaywallNavigationUrl,
   getInsufficientCreditsSubscriptionType,
   isChatDevelopmentEnvironment,
-  openChatInExternalBrowser,
-  recordExternalBrowserPromptShown,
-  resolveExternalBrowserPromptEligibility,
   shouldStartExternalBrowserPrompt,
 } from "./chat-screen.helpers";
 import styles from "./components/chat-screen.module.css";