Update admin theme/layout and refresh README details.

Align the project baseline with the latest admin interface styling and layout structure while documenting setup and usage updates in README.

infra/nginx/default.conf

@@ -0,0 +1,18 @@
+server {
+    listen 80;
+
+    add_header X-Content-Type-Options "nosniff" always;
+    add_header X-Frame-Options "DENY" always;
+    add_header Strict-Transport-Security "max-age=63072000; includeSubDomains; preload" always;
+    add_header Referrer-Policy "strict-origin-when-cross-origin" always;
+    add_header Permissions-Policy "camera=(), microphone=(), geolocation=()" always;
+    add_header Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline' https://fonts.googleapis.com; font-src 'self' https://fonts.gstatic.com; img-src 'self' data:; connect-src 'self'; frame-ancestors 'none'; base-uri 'self'; form-action 'self';" always;
+
+    location /api/ {
+        proxy_pass http://api:8000;
+    }
+
+    location / {
+        proxy_pass http://web:5173;
+    }
+}