Add production Dockerfiles and nginx config

Backend: installs non-editable, runs uvicorn without reload.
Frontend: multi-stage build, serves static files via nginx with
API proxy to the backend service and SPA fallback routing.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/nginx.conf

@@ -0,0 +1,20 @@
+server {
+    listen 80;
+
+    root /usr/share/nginx/html;
+    index index.html;
+
+    # Proxy API requests to the backend service
+    location /api/ {
+        proxy_pass http://api:8000;
+        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;
+    }
+
+    # Serve static files, fall back to index.html for SPA routing
+    location / {
+        try_files $uri $uri/ /index.html;
+    }
+}