fix: make the web bundle run and repair broken route declarations

- add babel.config.js with unstable_transformImportMeta: zustand/middleware ships
  import.meta.env, which the Metro web bundle (a classic script) cannot parse, so
  every page threw 'SyntaxError: Cannot use import.meta outside a module' and the
  app never hydrated after the static export.
- declare the settings screen as 'settings/index' in the root stack: the old name
  'settings' matched no route, so the modal presentation and the 'Settings' title
  were silently dropped (expo-router logged 'No route named settings exists').
- add the missing app/+not-found.tsx that the root layout already referenced.
- update the About label from LocalAiApp to LocalMind.

app/+not-found.tsx

@@ -0,0 +1,38 @@
+import { Link, Stack } from 'expo-router';
+import { StyleSheet, Text, View } from 'react-native';
+
+export default function NotFoundScreen() {
+  return (
+    <>
+      <Stack.Screen options={{ title: 'Oops!' }} />
+      <View style={styles.container}>
+        <Text style={styles.title}>This screen does not exist.</Text>
+
+        <Link href="/" style={styles.link}>
+          <Text style={styles.linkText}>Go to home screen</Text>
+        </Link>
+      </View>
+    </>
+  );
+}
+
+const styles = StyleSheet.create({
+  container: {
+    flex: 1,
+    alignItems: 'center',
+    justifyContent: 'center',
+    padding: 20,
+  },
+  title: {
+    fontSize: 20,
+    fontWeight: 'bold',
+  },
+  link: {
+    marginTop: 15,
+    paddingVertical: 15,
+  },
+  linkText: {
+    fontSize: 14,
+    color: '#2e78b7',
+  },
+});