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/_layout.tsx

@@ -28,7 +28,7 @@ export default function RootLayout() {
       <Stack>
         <Stack.Screen name="index" options={{ headerShown: false }} />
         <Stack.Screen name="chat" options={{ headerShown: false }} />
-        <Stack.Screen name="settings" options={{ presentation: 'modal', title: 'Settings' }} />
+        <Stack.Screen name="settings/index" options={{ presentation: 'modal', title: 'Settings' }} />
         <Stack.Screen name="+not-found" />
       </Stack>
       <StatusBar style={isDark ? 'light' : 'dark'} />