CUB-66: scaffold Angular frontend and add Dockerfile with nginx

- Scaffolded Angular 21 app in frontend/ (standalone, routing, scss)
- Multi-stage Dockerfile: node:22-alpine build → nginx:alpine serve
- nginx.conf with SPA routing fallback, API proxy, gzip, asset caching
- .dockerignore excludes node_modules, dist, .angular, spec files
- docker build → PASS, container serves UI on port 80 (HTTP 200)
- Final image: 92.9MB (nginx:alpine)

frontend/nginx.conf

@@ -0,0 +1,42 @@
+server {
+    listen 80;
+    server_name _;
+    root /usr/share/nginx/html;
+    index index.html;
+
+    # Gzip compression
+    gzip on;
+    gzip_types text/plain text/css application/json application/javascript text/xml application/xml text/javascript;
+    gzip_min_length 256;
+
+    # Angular SPA — fallback to index.html for client-side routing
+    location / {
+        try_files $uri $uri/ /index.html;
+    }
+
+    # Cache static assets aggressively
+    location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff2?|ttf|eot)$ {
+        expires 1y;
+        add_header Cache-Control "public, immutable";
+    }
+
+    # Proxy API requests to backend
+    # Uses resolver so nginx doesn't crash if backend isn't available at startup
+    resolver 127.0.0.11 valid=30s ipv6=off;
+    set $backend "extrudex-api:8080";
+
+    location /api/ {
+        proxy_pass http://$backend;
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+    }
+
+    # Health check endpoint
+    location /health {
+        access_log off;
+        return 200 "ok";
+        add_header Content-Type text/plain;
+    }
+}