Clean working version: deployed TypeScript backend + JSX frontend

- Replace old JS backend with working TypeScript backend from deployed containers
- Backend: Fastify + better-sqlite3 + Yjs CRDT, 17 TS source files, 13 test files
- Frontend: React JSX with fabric.js CAD canvas, vite build, nginx serving
- Fix nginx proxy port 5000→3001 to match backend
- Fix docker-compose port mapping 5000→3001
- Fix vite dev proxy port 5000→3001
- Add backend healthcheck to docker-compose
- Update index.html title to 'Web CAD', lang to 'de'
- Add .a0/ to .gitignore
- Remove old JS backend files (models, routes, config, middleware, seed)
- Remove tracked build artifacts (backend/public/)

backend/tsconfig.json

@@ -0,0 +1,14 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "outDir": "./dist",
+    "rootDir": "./src"
+  },
+  "include": ["src"]
+}