ci: scheduled workflows run on the cron lane runner

astra, heartbeat, housekeeping, sync, update and venture move to runs-on: cron
(green-tea-runner-cron), so they never queue ahead of deploys on the main runner.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VVFi3wvLWKaEkpDw6eLnQC

.github/workflows/heartbeat.yml

@@ -23,7 +23,7 @@ jobs:
       (github.event_name != 'issue_comment' || (github.event.issue.pull_request && github.event.comment.user.login != 'gitea-actions' &&
         (startsWith(github.event.comment.body, '**Approve') || startsWith(github.event.comment.body, 'Approve') ||
          startsWith(github.event.comment.body, '**Object') || startsWith(github.event.comment.body, 'Object'))))
-    runs-on: ubuntu-latest
+    runs-on: cron
     timeout-minutes: 55   # workers can overlap inside one job now (#75); under the hourly cadence, and the concurrency group queues the next run
     steps:
       - uses: actions/checkout@v5