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/src/knowledge.ts

@@ -0,0 +1,19 @@
+import { readdirSync, readFileSync } from 'node:fs';
+import { join } from 'node:path';
+
+let cached: string | undefined;
+
+/**
+ * The knowledge base is a set of Markdown files bundled with the Lambda.
+ * They are concatenated and injected as system instructions. RAG (selective
+ * retrieval) can replace this later without changing the API surface.
+ */
+export function loadKnowledgeBase(): string {
+  if (cached !== undefined) return cached;
+  const dir = process.env.KNOWLEDGE_DIR ?? join(import.meta.dirname, '..', 'knowledge');
+  const files = readdirSync(dir)
+    .filter((f) => f.endsWith('.md'))
+    .sort();
+  cached = files.map((f) => readFileSync(join(dir, f), 'utf-8')).join('\n\n---\n\n');
+  return cached;
+}