feat(mobile): add kill switch gate in root layout

mobile/src/app/_layout.tsx

@@ -1,19 +1,43 @@
-import { useEffect } from 'react';
+import { useEffect, useState } from 'react';
 import { Stack } from 'expo-router';
 import { StatusBar } from 'expo-status-bar';
+import { Text, View } from 'react-native';
 import { useAuthStore, type AuthState } from '../store/auth-store';
 import { useInboxStore, type InboxState } from '../store/inbox-store';
 import { useNotesStore, type NotesState } from '../store/notes-store';
 import { useWorkspaceStore, type WorkspaceState } from '../store/workspace-store';
-import { initPlatform } from '../lib/platform';
+import { checkKillSwitch, initPlatform } from '../lib/platform';
+import { colors } from '../theme';
 
 export default function RootLayout() {
+  const [killSwitchState, setKillSwitchState] = useState<{
+    checked: boolean;
+    disabled: boolean;
+    message: string | null;
+  }>({
+    checked: false,
+    disabled: false,
+    message: null,
+  });
+
   const bootstrapAuth = useAuthStore((state: AuthState) => state.bootstrap);
   const hydrateInbox = useInboxStore((state: InboxState) => state.hydrate);
   const hydrateNotes = useNotesStore((state: NotesState) => state.hydrate);
   const hydrateWorkspaces = useWorkspaceStore((state: WorkspaceState) => state.hydrate);
 
   useEffect(() => {
+    void checkKillSwitch()
+      .then((state) => {
+        setKillSwitchState({
+          checked: true,
+          disabled: state.disabled,
+          message: state.message,
+        });
+      })
+      .catch(() => {
+        setKillSwitchState({ checked: true, disabled: false, message: null });
+      });
+
     void bootstrapAuth();
     void initPlatform();
     void hydrateNotes();
@@ -21,6 +45,29 @@ export default function RootLayout() {
     void hydrateInbox();
   }, [bootstrapAuth, hydrateInbox, hydrateNotes, hydrateWorkspaces]);
 
+  if (killSwitchState.checked && killSwitchState.disabled) {
+    return (
+      <View
+        style={{
+          flex: 1,
+          alignItems: 'center',
+          justifyContent: 'center',
+          paddingHorizontal: 24,
+          backgroundColor: colors.bgCanvas,
+          gap: 12,
+        }}
+      >
+        <StatusBar style="light" />
+        <Text style={{ color: colors.textPrimary, fontSize: 24, fontWeight: '700', textAlign: 'center' }}>
+          NoteLett is temporarily unavailable
+        </Text>
+        <Text style={{ color: colors.textSecondary, fontSize: 15, textAlign: 'center' }}>
+          {killSwitchState.message ?? 'Service access is currently paused by the platform team. Please try again later.'}
+        </Text>
+      </View>
+    );
+  }
+
   return (
     <>
       <StatusBar style="light" />