Add Docker Compose deployment with multi-stage build and nginx

Multi-stage Dockerfile builds the Vite app in Node 22 and serves static
assets from nginx:alpine. Includes gzip compression, SPA fallback routing,
immutable cache headers for hashed assets, and configurable port mapping
(default 8080). Deploy with `docker compose up -d`.

nginx.conf

@@ -0,0 +1,21 @@
+server {
+    listen 80;
+    root /usr/share/nginx/html;
+    index index.html;
+
+    # Gzip compression
+    gzip on;
+    gzip_types text/html text/css application/javascript application/json;
+    gzip_min_length 256;
+
+    # Hashed assets — cache forever
+    location /assets/ {
+        add_header Cache-Control "public, max-age=31536000, immutable";
+    }
+
+    # SPA fallback — no-cache on index.html
+    location / {
+        add_header Cache-Control "no-cache";
+        try_files $uri $uri/ /index.html;
+    }
+}