refactor(skills): cleanup dead code + full workflow A→B→C→D integration

Cleanup:
- Remove unused validate_yaml() helper from lib.sh
- Remove USER_MANUAL.html + mqtt-broker-setup.html (no refs found)

Workflow A (create_session ↔ delegate-job):
- Add --submit-job <prompt> option to create_session.sh
- Auto-register session in delegate-job registry, store delegate_job_id in YAML

Workflow B (push-based monitor):
- Migrate reconcile.sh to MQTT subscriber mode (polling fallback preserved)

Workflow C (unified status):
- status.sh now shows session + delegate-job state in single column

Workflow D (audit log + perms):
- JSON job files chmod 600
- create/delete/resume now publish lifecycle events to delegate-job

skills/delegate-job/scripts/mqtt_common.py

@@ -260,6 +260,10 @@ def _atomic_write_record(job_id: str, registry_dir: str, record: Dict[str, Any])
             fh.flush()
             os.fsync(fh.fileno())
         os.replace(tmp, path)
+        try:
+            os.chmod(path, 0o600)
+        except Exception:
+            pass
     except BaseException:
         if os.path.exists(tmp):
             os.unlink(tmp)