chore: revert node-runner to stock image, remove Dockerfile

- Reverted to node:22-bookworm (no custom image)
- Removed Dockerfile.node (no CI to build it)
- Docker install step in riotpiao workflow is already the workaround

k8s/infra/forgejo-runner/Dockerfile.node

@@ -1,13 +0,0 @@
-FROM node:22-bookworm
-
-# Install Docker client (dind sidecar provides the daemon)
-RUN apt-get update && \
-    apt-get install -y --no-install-recommends \
-      docker.io \
-      git \
-      curl \
-      ca-certificates && \
-    rm -rf /var/lib/apt/lists/*
-
-# Verify installation
-RUN docker --version && node --version