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

services/api/test/usage.test.ts

@@ -0,0 +1,32 @@
+import { describe, expect, it } from 'vitest';
+import { canSendMessage, shouldResetUsage } from '../src/usage.js';
+
+describe('canSendMessage', () => {
+  it('allows messages under the free limit', () => {
+    expect(canSendMessage(0, 'free', 50)).toBe(true);
+    expect(canSendMessage(49, 'free', 50)).toBe(true);
+  });
+
+  it('blocks free users at the limit', () => {
+    expect(canSendMessage(50, 'free', 50)).toBe(false);
+    expect(canSendMessage(51, 'free', 50)).toBe(false);
+  });
+
+  it('never blocks active subscribers', () => {
+    expect(canSendMessage(10_000, 'active', 50)).toBe(true);
+  });
+});
+
+describe('shouldResetUsage', () => {
+  const day = 24 * 60 * 60 * 1000;
+
+  it('does not reset within the window', () => {
+    const now = new Date();
+    expect(shouldResetUsage(new Date(now.getTime() - 29 * day), now, 30)).toBe(false);
+  });
+
+  it('resets once the window has passed', () => {
+    const now = new Date();
+    expect(shouldResetUsage(new Date(now.getTime() - 30 * day), now, 30)).toBe(true);
+  });
+});