fix(ci): default reusable workflows onto evalops-private-ci

Blacksmith is retired and ubuntu-latest is billing-blocked for private
org repos. Callers that omit runner_label were still landing on those
defaults (Codex Rails historically blacksmith-4vcpu-ubuntu-2404, then
ubuntu-latest). Point the reusable defaults at owned private-CI ARC.

Author: haasonsaas

.github/workflows/agent-authorship-label.yml

@@ -19,7 +19,7 @@ on:
         description: "Runner label used for the label job"
         required: false
         type: string
-        default: ubuntu-latest
+        default: evalops-private-ci
       helper_ref:
         description: "evalops/.github ref used to checkout helper scripts"
         required: false

.github/workflows/codex-rails-check.yml

@@ -27,17 +27,17 @@ on:
         type: boolean
         default: false
       runner_label:
-        description: "Runner label used for the validation job"
+        description: "Runner label used for the validation job (owned private-CI ARC; never blacksmith-* or ubuntu-latest)"
         required: false
         type: string
-        default: ubuntu-latest
+        default: evalops-private-ci
 
 permissions:
   contents: read
 
 jobs:
   validate:
-    runs-on: ${{ inputs.runner_label || 'ubuntu-latest' }}
+    runs-on: ${{ inputs.runner_label || 'evalops-private-ci' }}
     timeout-minutes: 10
     steps:
       - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5

.github/workflows/review-thread-guard.yml

@@ -20,10 +20,10 @@ on:
         default: "high"
         type: string
       runner_label:
-        description: "Runner label used for the validation job"
+        description: "Runner label used for the validation job (owned private-CI ARC; never blacksmith-* or ubuntu-latest)"
         required: false
         type: string
-        default: ubuntu-latest
+        default: evalops-private-ci
       guard_ref:
         description: "evalops/.github ref to checkout for guard scripts"
         required: false
@@ -68,7 +68,7 @@ permissions:
 
 jobs:
   unresolved-review-threads:
-    runs-on: ${{ inputs.runner_label || 'ubuntu-latest' }}
+    runs-on: ${{ inputs.runner_label || 'evalops-private-ci' }}
     timeout-minutes: 5
     steps:
       - uses: actions/checkout@v5