Bygg NeuroSemantics AI: minimal mobilapp, en backend, IaC och CI/CD

Ersätter den tidigare webappen på denna branch med ett fokuserat monorepo:

- apps/mobile: Expo/React Native med tre vyer (Welcome, Chat, Paywall),
  Cognito hosted UI-inloggning (Apple/Google/e-post) och In-App
  Purchase/Play Billing via en gemensam purchases-modul.
- services/api: en enda Lambda-backend — OpenAI Responses API med
  Markdown-kunskapsbas som systeminstruktioner, free tier-gräns i
  PostgreSQL (HTTP 402 -> paywall) och kvittoverifiering bakom ett
  delat PaymentProvider-interface (Apple/Google, Stripe kan läggas
  till för webb senare).
- infra: AWS CDK-stack med API Gateway (JWT-authorizer), Lambda,
  Cognito, Aurora Serverless v2 och Secrets Manager.
- db/migrations: minimal datamodell (users + usage), inga
  konversationer sparas.
- GitHub Actions: CI (lint, typecheck, test) och deploy från main.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0118DaxZR36RpnY524vRqx3z

apps/mobile/App.tsx

@@ -0,0 +1,29 @@
+import { useEffect, useState } from 'react';
+import { StatusBar } from 'expo-status-bar';
+import { getAccessToken } from './src/auth/session';
+import { ChatScreen } from './src/screens/ChatScreen';
+import { PaywallScreen } from './src/screens/PaywallScreen';
+import { WelcomeScreen } from './src/screens/WelcomeScreen';
+
+type View = 'loading' | 'welcome' | 'chat' | 'paywall';
+
+/**
+ * Three views, no navigation library. The backend decides when the paywall
+ * appears (HTTP 402 on /chat).
+ */
+export default function App() {
+  const [view, setView] = useState<View>('loading');
+
+  useEffect(() => {
+    getAccessToken().then((token) => setView(token ? 'chat' : 'welcome'));
+  }, []);
+
+  return (
+    <>
+      <StatusBar style="dark" />
+      {view === 'welcome' && <WelcomeScreen onSignedIn={() => setView('chat')} />}
+      {view === 'chat' && <ChatScreen onLimitReached={() => setView('paywall')} />}
+      {view === 'paywall' && <PaywallScreen onSubscribed={() => setView('chat')} />}
+    </>
+  );
+}