Escape \$PHPIZE_DEPS in php-Dockerfile template

Build failed: groovy.lang.MissingPropertyException: No such property:
PHPIZE_DEPS. This whole file is rendered through
constructTemplate.groovy's SimpleTemplateEngine before it ever becomes
a real Dockerfile — bare $IDENTIFIER is Groovy GString interpolation
syntax, same as ${IDENTIFIER}, so it tried resolving PHPIZE_DEPS
against the render binding (which only has `version`) instead of
leaving it as literal shell syntax for docker-php-ext-install to
expand at RUN time. \$ is the correct escape for a literal dollar sign
in SimpleTemplateEngine output.

resources/com/homelab/php-Dockerfile

@@ -17,9 +17,17 @@
 # extensions on Alpine (unlike the Debian image, which had them
 # preinstalled) — installed as a virtual package and removed again
 # right after, so the final image doesn't carry build tooling.
+# \$PHPIZE_DEPS escaped (not ${PHPIZE_DEPS} or bare $PHPIZE_DEPS) —
+# this whole file goes through constructTemplate.groovy's
+# SimpleTemplateEngine first, which treats bare $IDENTIFIER the same
+# as ${IDENTIFIER} (Groovy GString interpolation syntax) and tried to
+# resolve it against the render binding (which only has `version`),
+# throwing MissingPropertyException before this ever became a real
+# Dockerfile. \$ survives the template pass as a literal $, which is
+# what the shell needs to actually expand this at RUN time.
 FROM harbor.192.168.1.7.nip.io/base-images/php:${version}-cli-alpine
 WORKDIR /var/www/html
-RUN apk add --no-cache --virtual .build-deps $PHPIZE_DEPS \
+RUN apk add --no-cache --virtual .build-deps \$PHPIZE_DEPS \
     && docker-php-ext-install pdo pdo_mysql \
     && apk del .build-deps
 COPY . .