Replace Next.js app with Vite React app (gerbil-manager-web)

- Remove gerbil-manager-nextjs (unused scaffold; recoverable from history)
- Scaffold gerbil-manager-web: Vite + React 19 + TypeScript
- German-only UI (lang=de, central strings in src/strings/de.ts)
- Mobile-first shell: bottom tab bar on phones, sidebar on >=768px
- react-router with skeleton routes (Start, Rennmaeuse, Wuerfe, Zuechter)
- API client (src/api/client.ts) pointing at GerbilManagerWebAPI,
  configurable via VITE_API_BASE_URL (default http://localhost:5179)
- nginx-based Dockerfile with SPA fallback; docker-compose frontend
  service now builds gerbil-manager-web

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

gerbil-manager-web/tsconfig.node.json

@@ -0,0 +1,24 @@
+{
+  "compilerOptions": {
+    "tsBuildInfoFile": "./node_modules/.tmp/tsconfig.node.tsbuildinfo",
+    "target": "es2023",
+    "lib": ["ES2023"],
+    "module": "esnext",
+    "types": ["node"],
+    "skipLibCheck": true,
+
+    /* Bundler mode */
+    "moduleResolution": "bundler",
+    "allowImportingTsExtensions": true,
+    "verbatimModuleSyntax": true,
+    "moduleDetection": "force",
+    "noEmit": true,
+
+    /* Linting */
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
+    "erasableSyntaxOnly": true,
+    "noFallthroughCasesInSwitch": true
+  },
+  "include": ["vite.config.ts"]
+}