ci: fix runner labels + CoreDNS rewrite + cleanup

- Runners use public images (code.forgejo.org/forgejo/runner:6)
- Labels pull from Docker Hub: golang:1.26, node:22, rust:1-bookworm
- Add CoreDNS api.riotpiao.com rewrite
- Fix runner re-registration to keep labels in sync
- Add unified CI pattern docs to CLAUDE.example.md
- Remove dead .forgejo/ workflow dir (Forgejo uses .gitea/)

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

@@ -2,20 +2,16 @@
 # runner instance. Only runner.name and runner.labels differ -- everything
 # else (image, dind, persistence, tolerations, nodeSelector) is shared.
 #
-# Use docker:27-cli instead of rust:1.83-bookworm because:
-#   - Needs Node.js for GitHub Actions (actions/checkout@v4, etc.)
-#   - Has docker CLI + git + full dev tools
-#   - rust:1.83-bookworm lacks Node.js (causes action failures)
-#
-# docker:27-cli verified: docker manifest inspect docker:27-cli ✓
+# Label image: rust:1-bookworm — Debian, root, apt-get, Rust, cargo, git.
+# Install Node.js/docker in workflow steps as needed.
 runner:
+  image:
+    repository: code.forgejo.org/forgejo/runner
+    tag: "6"
   name: rust-runner
-  labels: "rust:docker://docker:27-cli"
+  labels: "rust:docker://rust:1-bookworm"
+
 
-persistence:
-  reg:
-    storageClass: longhorn
-    size: 20Gi
 
 # GC CronJob renders only from the default (golang) values to avoid duplicates
 gc: