Set HUGO_CACHEDIR and WORKDIR in the builder image

The official Hugo image ships ENV HUGO_CACHEDIR=/cache. deploy.sh reads
${HUGO_CACHEDIR:-/tmp/hugo_cache}, so the default never fires and the cache
lands in the container's writable layer rather than the volume mounted at
/tmp: discarded on every run, and consuming host disk in between. The
floryn90 image it replaces put the cache on /tmp, which is why this did not
bite before.

Set WORKDIR to /src for the same reason — upstream sets /project, which is
not where the Jenkins workspace is mounted. deploy.sh cds to $SRC either way,
but the image should not disagree with the service it runs in.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01X1AuLA5tHPwpD7Hp5utPkS

Author: Robbie1977

Dockerfile

@@ -27,5 +27,14 @@ FROM ghcr.io/gohugoio/hugo:v0.164.0
 USER root
 RUN apk add --no-cache bash rsync findutils
 
+# The upstream image sets HUGO_CACHEDIR=/cache and WORKDIR /project. Both are
+# wrong here and neither can be left to deploy.sh's defaults: the script uses
+# ${HUGO_CACHEDIR:-/tmp/hugo_cache}, which never fires while the image has the
+# variable set, so the cache would land in the container's writable layer
+# instead of the volume mounted at /tmp — discarded every run, and growing host
+# disk in between. Rancher mounts the workspace at /src and the cache at /tmp.
+ENV HUGO_CACHEDIR=/tmp/hugo_cache
+WORKDIR /src
+
 ENTRYPOINT []
 CMD ["/bin/bash", "/src/deploy.sh"]