Add nginx (closes #11)

Install nginx from apt and check nginx -v in the smoke test.

Model: deepseek-v4-pro

build.sh

@@ -32,7 +32,8 @@ apt-get -y install --no-install-recommends \
     libvips-dev libvips-tools libheif-dev libheif-plugin-aomenc \
     imagemagick ghostscript \
     ruby ruby-dev bundler \
-    valkey-server valkey-tools postgresql
+    valkey-server valkey-tools postgresql \
+    nginx
 
 # --- Go (latest) -------------------------------------------------------------
 gover="$(curl -fsSL 'https://go.dev/VERSION?m=text' | head -n1)"
@@ -149,6 +150,7 @@ bundle --version
 valkey-server --version
 valkey-cli --version
 psql --version
+nginx -v
 hugo version
 node --version
 npm --version