chore: projekt-scaffold mit next 15, tailwind und shadcn/ui

Next.js 15 (App Router, TypeScript strict), Tailwind CSS 4 und
shadcn/ui als Basis. Standalone-Output und serverExternalPackages
sind fuer den spaeteren Docker-Build vorbereitet.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,42 @@
+# dependencies
+/node_modules
+/.pnp
+.pnp.*
+.yarn/*
+
+# next.js
+/.next/
+/out/
+/build
+next-env.d.ts
+
+# testing
+/coverage
+/test-results
+/playwright-report
+/blob-report
+/playwright/.cache
+
+# runtime data (database, uploads) - never in git, this is the backup target
+/data
+
+# production
+*.tsbuildinfo
+
+# misc
+.DS_Store
+*.pem
+Thumbs.db
+
+# debug
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+.pnpm-debug.log*
+
+# env files
+.env
+.env*.local
+
+# vercel
+.vercel