chore: planning docs + backend/frontend scaffold + MVP Prisma schema

- CLAUDE.md, ARCHITECTURE.md, TASKS.md per Lastenheft-Vorgabe
- ApiCore-Backend: NestJS scaffold, Prisma 7 (DATABASE_URL via prisma.config.ts)
- ApiCore-Frontend: Next.js App Router scaffold (TS, Tailwind, ESLint)
- prisma/schema.prisma: alle MVP-Entitaeten aus Abschnitt 13/4.2-4.22/26,
  validiert und Client generiert

Grundgeruest (TASKS.md #0) noch nicht vollstaendig: shadcn/ui, TanStack Query,
PWA-Manifest, deploy/k8s/, Dockerfiles fehlen noch.

ApiCore-Backend/test/app.e2e-spec.ts

@@ -0,0 +1,29 @@
+import { Test, TestingModule } from '@nestjs/testing';
+import { INestApplication } from '@nestjs/common';
+import request from 'supertest';
+import { App } from 'supertest/types';
+import { AppModule } from './../src/app.module';
+
+describe('AppController (e2e)', () => {
+  let app: INestApplication<App>;
+
+  beforeEach(async () => {
+    const moduleFixture: TestingModule = await Test.createTestingModule({
+      imports: [AppModule],
+    }).compile();
+
+    app = moduleFixture.createNestApplication();
+    await app.init();
+  });
+
+  it('/ (GET)', () => {
+    return request(app.getHttpServer())
+      .get('/')
+      .expect(200)
+      .expect('Hello World!');
+  });
+
+  afterEach(async () => {
+    await app.close();
+  });
+});