feat(auth): add cold-start token verification with loading state to app layout

Move token verification from root layout SessionGate to (app) group layout,
enabling cold-start verification without blocking public pages (privacy/terms).
Show ActivityIndicator while verification is in progress, then redirect to
login if unverified.

BREAKING CHANGE: Authentication flow changed - token verification now occurs
in the (app) layout group instead of root layout SessionGate wrapper.

app/_layout.tsx

@@ -1,5 +1,5 @@
 import '../src/polyfills';
-import React, { useEffect, useRef, useState } from 'react';
+import React, { useEffect, useRef } from 'react';
 import { AppState, AppStateStatus, Platform, View, ActivityIndicator } from 'react-native';
 import { Stack, useRouter } from 'expo-router';
 import { StatusBar } from 'expo-status-bar';
@@ -11,8 +11,6 @@ import * as SystemUI from 'expo-system-ui';
 import { useFonts } from 'expo-font';
 
 import { registerNotificationPresentationHandler } from '@/services/notification';
-import { api } from '@/services/core';
-import { wsService } from '@/services/core';
 import { EventSubscriber } from '../src/infrastructure/EventSubscriber';
 import {
   ThemeBootstrap,
@@ -24,7 +22,6 @@ import {
 import AppPromptBar from '../src/components/common/AppPromptBar';
 import AppDialogHost from '../src/components/common/AppDialogHost';
 import { installAlertOverride } from '@/services/ui';
-import { useAuthStore } from '../src/stores';
 import { checkForAPKUpdate } from '@/services/platform';
 import { CallScreen, IncomingCallModal, FloatingCallWindow } from '../src/components/call';
 import { jpushService } from '@/services/notification/jpushService';
@@ -104,36 +101,6 @@ function SystemChrome() {
   return null;
 }
 
-function SessionGate({ children }: { children: React.ReactNode }) {
-  const isAuthenticated = useAuthStore((s) => s.isAuthenticated);
-  const fetchCurrentUser = useAuthStore((s) => s.fetchCurrentUser);
-  const colors = useAppColors();
-  const [verified, setVerified] = useState(false);
-
-  useEffect(() => {
-    fetchCurrentUser().finally(() => setVerified(true));
-  }, [fetchCurrentUser]);
-
-  // If persisted state shows authenticated, render immediately (background verify)
-  // If not authenticated and not yet verified, show loading
-  if (!isAuthenticated && !verified) {
-    return (
-      <View
-        style={{
-          flex: 1,
-          justifyContent: 'center',
-          alignItems: 'center',
-          backgroundColor: colors.background.default,
-        }}
-      >
-        <ActivityIndicator size="large" color={colors.primary.main} />
-      </View>
-    );
-  }
-  // If verified and not authenticated, the Redirect in (app)/_layout.tsx handles it
-  return <>{children}</>;
-}
-
 function NotificationBootstrap() {
   const appState = useRef<AppStateStatus>(AppState.currentState);
   const permissionRequested = useRef(false);
@@ -280,18 +247,16 @@ function ThemedStack() {
       <StatusBar style={resolved === 'dark' ? 'light' : 'dark'} />
       <SystemChrome />
       <EventSubscriber />
-      <SessionGate>
-        <NotificationBootstrap />
-        <APKUpdateBootstrap />
-        <CallKeepBootstrap />
-        <Stack screenOptions={{ headerShown: false }}>
-          <Stack.Screen name="index" options={{ headerShown: false }} />
-          <Stack.Screen name="(auth)" options={{ headerShown: false }} />
-          <Stack.Screen name="(app)" options={{ headerShown: false }} />
-          <Stack.Screen name="privacy" options={{ headerShown: false }} />
-          <Stack.Screen name="terms" options={{ headerShown: false }} />
-        </Stack>
-      </SessionGate>
+      <NotificationBootstrap />
+      <APKUpdateBootstrap />
+      <CallKeepBootstrap />
+      <Stack screenOptions={{ headerShown: false }}>
+        <Stack.Screen name="index" options={{ headerShown: false }} />
+        <Stack.Screen name="(auth)" options={{ headerShown: false }} />
+        <Stack.Screen name="(app)" options={{ headerShown: false }} />
+        <Stack.Screen name="privacy" options={{ headerShown: false }} />
+        <Stack.Screen name="terms" options={{ headerShown: false }} />
+      </Stack>
     </>
   );
 }