Upgrade k8s forgejo-runner from v6.3.1 to v12.7.0 (#251)

## Summary

Completes the `upgrade-k8s-runner` mikado chain. Both prerequisites (workflow validation in Dagger, config review against v12 defaults) were resolved in #250.

- Bump runner image `code.forgejo.org/forgejo/runner:6.3.1` → `12.7.0`
- Update `service-versions.yaml` to track new version
- Mark goal card complete (remove `status: active`)

## Deployment and Testing

After merge:
1. `argocd app sync forgejo-runner`
2. Verify runner registers in Forgejo admin → runners
3. Trigger a test workflow (e.g. `branch-cleanup.yaml` manual dispatch)

Rollback: revert image tag to `6.3.1`, push, sync.
Reviewed-on: https://forge.ops.eblu.me/eblume/blumeops/pulls/251

argocd/manifests/forgejo-runner/deployment.yaml

@@ -18,7 +18,7 @@ spec:
       containers:
         # Forgejo runner daemon
         - name: runner
-          image: code.forgejo.org/forgejo/runner:6.3.1
+          image: code.forgejo.org/forgejo/runner:12.7.0
           env:
             - name: TZ
               value: America/Los_Angeles

docs/changelog.d/upgrade-k8s-runner-v12.infra.md

@@ -0,0 +1 @@
+Upgrade k8s forgejo-runner daemon from v6.3.1 to v12.7.0

docs/how-to/forgejo-runner/upgrade-k8s-runner.md

@@ -1,6 +1,5 @@
 ---
 title: Upgrade K8s Forgejo Runner to v12
-status: active
 requires:
   - validate-workflows-against-v12
   - review-runner-config-v12

service-versions.yaml

@@ -187,7 +187,7 @@ services:
   - name: forgejo-runner
     type: argocd
     last-reviewed: 2026-02-22
-    current-version: "6.3.1"
+    current-version: "12.7.0"
     upstream-source: https://code.forgejo.org/forgejo/runner/releases
     notes: >-
       Runner daemon version. Job execution container (containers/forgejo-runner)