fix: preserve iframe plugin chat mode

frontend-web/src/pages/LoginPage.tsx

@@ -76,7 +76,6 @@ function summarizeStoredUserInfo(): Record<string, unknown> | null {
 }
 
 const DEFAULT_USERNAME = 'guest';
-const IFRAME_LOGIN_SOURCE = 'iframe';
 const IFRAME_CHAT_MODE = 'iframe';
 const DEFAULT_REDIRECT_PATH = '/page/workspace/chats/new';
 const FULL_CHAT_MODE = 'full';
@@ -104,15 +103,13 @@ export default function LoginPage() {
     searchParams.get('chatMode')?.trim().toLowerCase() ?? '';
   const brainyIframeRequested = requestedChatMode === IFRAME_CHAT_MODE;
   // Wujie is an application container, not the Brainy iframe protocol. It
-  // must therefore land on the regular full ChatPage. Legacy `from=iframe`
-  // links now do the same; only the explicit `chatMode=iframe` protocol opt-in
-  // is allowed to open IframeChatPage.
+  // must therefore land on the regular full ChatPage. Plugin links with
+  // `from=iframe` are normalized into the explicit iframe protocol mode.
   const fullChatRequested = useMemo(
     () =>
       !brainyIframeRequested &&
       (isWujieEnv() ||
-        requestedChatMode === FULL_CHAT_MODE ||
-        searchParams.get('from') === IFRAME_LOGIN_SOURCE),
+        requestedChatMode === FULL_CHAT_MODE),
     [brainyIframeRequested, requestedChatMode, searchParams],
   );
   const isIframeLogin = useMemo(