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/chat.ts

@@ -0,0 +1,62 @@
+import { config } from './config.js';
+import { getSecret } from './secrets.js';
+import { loadKnowledgeBase } from './knowledge.js';
+
+export interface ChatMessage {
+  role: 'user' | 'assistant';
+  content: string;
+}
+
+const BASE_INSTRUCTIONS = `You are NeuroSemantics AI — a calm, precise conversation partner
+specialized in neurosemantics and NLP (Neuro-Linguistic Programming).
+
+Principles:
+- Be warm but restrained. Short paragraphs. No filler, no hype.
+- Ground answers in the knowledge base below. If something is outside
+  neurosemantics/NLP, gently steer the conversation back.
+- Ask one clarifying question at a time when the user's goal is unclear.
+- You are not a therapist and do not diagnose. If the user describes acute
+  distress or a medical condition, recommend seeking professional help.
+- Answer in the language the user writes in.`;
+
+/**
+ * Calls the OpenAI Responses API with the knowledge base as system
+ * instructions and the conversation as input. Conversations are held by the
+ * client and passed through — nothing is persisted server-side.
+ */
+export async function generateReply(messages: ChatMessage[]): Promise<string> {
+  const appSecret = await getSecret(config.appSecretArn);
+  const apiKey = appSecret.OPENAI_API_KEY;
+  if (!apiKey) throw new Error('OPENAI_API_KEY missing from application secret');
+
+  const response = await fetch('https://api.openai.com/v1/responses', {
+    method: 'POST',
+    headers: {
+      Authorization: `Bearer ${apiKey}`,
+      'Content-Type': 'application/json',
+    },
+    body: JSON.stringify({
+      model: config.openAiModel,
+      instructions: `${BASE_INSTRUCTIONS}\n\n# Knowledge base\n\n${loadKnowledgeBase()}`,
+      input: messages.map((m) => ({ role: m.role, content: m.content })),
+    }),
+  });
+
+  if (!response.ok) {
+    const body = await response.text();
+    throw new Error(`OpenAI request failed (${response.status}): ${body}`);
+  }
+
+  const data = (await response.json()) as {
+    output?: { type: string; content?: { type: string; text?: string }[] }[];
+  };
+  const text = (data.output ?? [])
+    .filter((item) => item.type === 'message')
+    .flatMap((item) => item.content ?? [])
+    .filter((part) => part.type === 'output_text')
+    .map((part) => part.text ?? '')
+    .join('');
+
+  if (!text) throw new Error('OpenAI response contained no output text');
+  return text;
+}