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
 
 # Link the PostgreSQL server binaries onto PATH. They live under a versioned
 # directory (/usr/lib/postgresql/*/bin); the client psql is already on PATH.
@@ -145,8 +146,9 @@ rm -rf /usr/share/doc /usr/share/man /usr/share/info /usr/share/lintian
 find /usr/share/locale -mindepth 1 -maxdepth 1 ! -name 'en*' ! -name 'locale.alias' -exec rm -rf {} +
 rm -rf /root/.cache /root/.npm /root/.config /root/go /tmp/* /var/tmp/*
 
-# Valkey opens its log file at startup; recreate the log directory the
-# cleanup above removed, with its package owner.
+# nginx and Valkey open their log files at startup; recreate the log
+# directories the cleanup above removed, with their package owners.
+install -d -o root -g adm /var/log/nginx
 install -d -o valkey -g adm -m 2750 /var/log/valkey
 
 # --- sanity ------------------------------------------------------------------
@@ -170,6 +172,7 @@ valkey-cli ping
 valkey-cli shutdown nosave
 psql --version
 postgres --version
+nginx -t
 hugo version
 node --version
 npm --version