* chore(ops): runner-box janitor script + operations runbook (WS3.3)
Codifies what was manual discipline on the .113 self-hosted pool (two live
incidents on the v3.8.47 release day): 30min cron sweeping stale runner
temp/work dirs (>24h), disk-pressure alert at >=85% (SQLITE_FULL killed shards
mid-run), and the proven 4-runner ceiling on the 16 GB box (8-wide OOM'd jobs;
stopping a busy runner cancels its job — documented). Script smoke-tested live
(disk 82%, 1 active runner, exit 0); bash -n clean.
* docs(ops): reword error-code/bash-env mentions the fabricated-docs env detector misreads
* fix(ops): harden janitor sweep — no symlink follow, -xdev, narrowed patterns (root-cron on world-writable /tmp)
