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.

babel.config.js

@@ -0,0 +1,16 @@
+module.exports = function (api) {
+  api.cache(true);
+  return {
+    presets: [
+      [
+        'babel-preset-expo',
+        {
+          // Dependencias (zustand/middleware) usam `import.meta.env`, que nao existe
+          // no bundle web do Metro (script classico) e quebrava a hidratacao do app.
+          // O polyfill do Expo troca por `globalThis.__ExpoImportMetaRegistry`.
+          unstable_transformImportMeta: true,
+        },
+      ],
+    ],
+  };
+};