feat: custom forgejo-runner-node image with docker.io pre-installed

- Dockerfile.node extends node:22-bookworm + docker.io
- CI workflow builds and pushes to forgejo registry on changes
- values-node.yaml references custom image instead of stock node
- Removes need to install docker in every workflow using node runner

k8s/infra/forgejo-runner/Dockerfile.node

@@ -0,0 +1,13 @@
+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