refactor: simplify Docker and CI/CD to use unified config

- Replace symlinked Dockerfile with simplified version in root
- Reduce Docker build args (unified config provides defaults)
- Update CI/CD workflows to use minimal build arguments
- Add nginx.conf to root directory (replace docker/nginx.conf)
- Remove docker-bake references from CI/CD workflows
- Focus on essential runtime overrides only
- Let unified config handle smart defaults

nginx.conf

@@ -0,0 +1,49 @@
+server {
+    listen 80;
+    server_name localhost;
+    root /usr/share/nginx/html;
+    index index.html;
+
+    # Enable gzip compression
+    gzip on;
+    gzip_vary on;
+    gzip_min_length 1024;
+    gzip_proxied expired no-cache no-store private must-revalidate auth;
+    gzip_types
+        text/plain
+        text/css
+        text/xml
+        text/javascript
+        application/javascript
+        application/xml+rss
+        application/json;
+
+    # Security headers
+    add_header X-Frame-Options "SAMEORIGIN" always;
+    add_header X-Content-Type-Options "nosniff" always;
+    add_header X-XSS-Protection "1; mode=block" always;
+    add_header Referrer-Policy "no-referrer-when-downgrade" always;
+
+    # Handle React Router (SPA)
+    location / {
+        try_files $uri $uri/ /index.html;
+    }
+
+    # Cache static assets
+    location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2|ttf|eot)$ {
+        expires 1y;
+        add_header Cache-Control "public, immutable";
+    }
+
+    # Health check endpoint
+    location /health {
+        access_log off;
+        return 200 "healthy\n";
+        add_header Content-Type text/plain;
+    }
+
+    # Disable access to hidden files
+    location ~ /\. {
+        deny all;
+    }
+}