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/Dockerfile

@@ -1,13 +1,9 @@
-FROM node:22-alpine
-RUN apk add --no-cache curl
-
+FROM node:20-alpine
 WORKDIR /app
-
-COPY package*.json ./
-RUN npm ci --only=production
-
+RUN apk add --no-cache wget
+COPY package.json package-lock.json* ./
+RUN npm install
 COPY . .
-
-EXPOSE 5000
-
-CMD ["node", "server.js"]
+RUN npm run build
+EXPOSE 3001
+CMD ["node", "dist/index.js"]