bootstrap: use base images for runners, custom images via CI

- golang-runner: docker:27-cli (has Node.js + docker)
- rust-runner: docker:27-cli (bootstrap, CI adds Rust)
- node-runner: node:22-bookworm (has Node.js, CI adds docker)

CI workflow (.gitea/workflows/build-runner-images.yml):
1. Watches Dockerfile.* changes
2. Builds custom images with Node.js pre-installed
3. Pushes to registry
4. Image Updater detects and updates values.yaml
5. ArgoCD syncs to new custom images

This avoids token complexity - just push Dockerfile changes to git!

k8s/infra/forgejo-runner/values-rust.yaml

@@ -2,17 +2,13 @@
 # runner instance. Only runner.name and runner.labels differ -- everything
 # else (image, dind, persistence, tolerations, nodeSelector) is shared.
 #
-# Custom image: docker:27-cli + Node.js + Rust + build tools
-#   - Node.js for GitHub Actions (actions/checkout@v4, etc.)
-#   - Docker CLI for container builds
-#   - Rust toolchain (via rustup)
-#   - Build essentials
+# Bootstrap with base image, custom image via CI+Image Updater
 runner:
   image:
-    repository: forgejo.riotpiao.com/rock/forgejo-runner-rust
-    tag: "latest"  # Image Updater tracks and updates this
+    repository: docker
+    tag: "27-cli"
   name: rust-runner
-  labels: "rust:docker://forgejo.riotpiao.com/rock/forgejo-runner-rust:latest"
+  labels: "rust:docker://docker:27-cli"