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-Frontend/.gitignore

@@ -0,0 +1,41 @@
+# See https://help.github.com/articles/ignoring-files/ for more about ignoring files.
+
+# dependencies
+/node_modules
+/.pnp
+.pnp.*
+.yarn/*
+!.yarn/patches
+!.yarn/plugins
+!.yarn/releases
+!.yarn/versions
+
+# testing
+/coverage
+
+# next.js
+/.next/
+/out/
+
+# production
+/build
+
+# misc
+.DS_Store
+*.pem
+
+# debug
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+.pnpm-debug.log*
+
+# env files (can opt-in for committing if needed)
+.env*
+
+# vercel
+.vercel
+
+# typescript
+*.tsbuildinfo
+next-env.d.ts