fix(frontend): remediate Trivy vulnerabilities in build image

frontend/Dockerfile

@@ -18,6 +18,9 @@ LABEL maintainer="Sean Morley" \
 # The WORKDIR instruction sets the working directory for everything that will happen next
 WORKDIR /app
 
+# Upgrade zlib to include Alpine security fixes
+RUN apk upgrade --no-cache zlib
+
 # Install pnpm globally first
 RUN npm install -g pnpm
 
@@ -46,4 +49,4 @@ USER node:node
 EXPOSE 3000
 
 # Run startup.sh instead of the default command
-CMD ["./startup.sh"]
+CMD ["./startup.sh"]