fix: use proper language images for runner labels, not bare Alpine

ROOT CAUSE: All 3 runner labels pointed to code.forgejo.org/forgejo/runner:6
(bare Alpine). When Forgejo runs a workflow, it creates a container FROM the
label image — this container had no Node.js, no docker CLI, no Go/Rust,
no root access, and no apt-get. Every CI job failed.

FIX: Change runner labels to official Debian-based language images:
  golang → docker://golang:1.26-bookworm (Go + apt-get + root)
  node   → docker://node:22-bookworm (Node.js + npm + apt-get + root)
  rust   → docker://rust:1-bookworm (Rust + cargo + apt-get + root)

The runner daemon pod still uses forgejo/runner:6 — only the label image
(what workflow steps execute in) changes.

Unified CI pattern for ALL repos:
1. Install Node.js first if not present (needed for actions/checkout@v4)
2. Install docker.io via apt-get (needed for docker build/push)
3. Use actions/checkout@v4 normally
4. Build/push with docker

IMPORTANT: Runners must re-register after merge. Delete PVCs or
/data/.runner files to trigger re-registration with new labels.

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

@@ -2,13 +2,14 @@
 # runner instance. Only runner.name and runner.labels differ -- everything
 # else (image, dind, persistence, tolerations, nodeSelector) is shared.
 #
-# Bootstrap with runner image, CI builds custom with Node.js+Rust
+# 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://code.forgejo.org/forgejo/runner:6"
+  labels: "rust:docker://rust:1-bookworm"