Add tzdata (closes #4)

Install tzdata from apt so the time zone database is present at run
time, and check a zone lookup in the smoke test.

Model: deepseek-v4-pro

README.md

@@ -34,6 +34,7 @@ Image: `git.eeqj.de/sneak/baseimage`, built for `linux/amd64` and
 | pyenv           | git tag                        | `/usr/local/pyenv`             |
 | Python (latest) | `pyenv install`                | `/usr/local/pyenv/versions/*`  |
 | virtualenv      | apt, and pip in pyenv Python   | `virtualenv` on `PATH`         |
+| tzdata          | apt                            | `/usr/share/zoneinfo`          |
 
 Plus the usual odds and ends: `git`, `curl`, `wget`, `jq`, `rsync`,
 `openssh-client`, `zip`/`unzip`, `xz-utils`, `bzip2`, and the `-dev`

bin/test

@@ -23,6 +23,7 @@ docker run --rm "$img" bash -ec '
     prettier --version
     shellcheck --version
     govulncheck -version
+    TZ=America/New_York date +%Z
 '
 
 echo "== $img: runit service lifecycle"

build.sh

@@ -26,7 +26,8 @@ apt-get -y install --no-install-recommends \
     libbz2-dev libffi-dev libgdbm-dev liblzma-dev libncurses-dev \
     libreadline-dev libsqlite3-dev libssl-dev libxml2-dev libxmlsec1-dev \
     tk-dev uuid-dev zlib1g-dev \
-    shellcheck
+    shellcheck \
+    tzdata
 
 # --- Go (latest) -------------------------------------------------------------
 gover="$(curl -fsSL 'https://go.dev/VERSION?m=text' | head -n1)"
@@ -104,6 +105,7 @@ go version
 govulncheck -version
 golangci-lint version
 shellcheck --version
+TZ=America/New_York date +%Z
 hugo version
 node --version
 npm --version