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/src/app.module.ts

@@ -0,0 +1,10 @@
+import { Module } from '@nestjs/common';
+import { AppController } from './app.controller';
+import { AppService } from './app.service';
+
+@Module({
+  imports: [],
+  controllers: [AppController],
+  providers: [AppService],
+})
+export class AppModule {}