Add zstd and the sqlite3 CLI (closes #5)

Install zstd and sqlite3 from apt and check both in the smoke test.

Model: deepseek-v4-pro

build.sh

@@ -27,7 +27,8 @@ apt-get -y install --no-install-recommends \
     libreadline-dev libsqlite3-dev libssl-dev libxml2-dev libxmlsec1-dev \
     tk-dev uuid-dev zlib1g-dev \
     shellcheck \
-    tzdata
+    tzdata \
+    zstd sqlite3
 
 # --- Go (latest) -------------------------------------------------------------
 gover="$(curl -fsSL 'https://go.dev/VERSION?m=text' | head -n1)"
@@ -104,6 +105,8 @@ govulncheck -version
 golangci-lint version
 shellcheck --version
 test -e /usr/share/zoneinfo/America/New_York
+zstd --version
+sqlite3 --version
 hugo version
 node --version
 npm --version