docs: add nginx install instructions to README step 12

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -207,6 +207,16 @@ npm run db:seed
 
 ### Step 12 — Configure nginx
 
+Install nginx:
+
+```sh
+sudo apt update
+sudo apt install -y nginx
+
+# Verify
+nginx -v
+```
+
 The repo includes `nginx.conf` in the project root. Install it as the active site config:
 
 ```sh