Pre-install pnpm 9.15.4 via corepack in the image so it doesn't
download every run. Use --config CLI flag instead of CONFIG_FILE
env var to ensure container.options volume mount is applied.
Build a runner-image based on node:20-bookworm with all CI tools
baked in, avoiding apt-get install in every workflow run. Runner
labels now point to gitea.coreworlds.io/lazorgurl/runner-image.