feat(#1165): async external_job_waiting half-state + resume/pause contract (#1221)

Core half of #1105: a legal external_job_waiting deferred state so an async-dispatched Execute step (committing a .planning/async-jobs/<job>.json manifest, deferring SUMMARY.md) is not an illegal partial. execute-phase safe-resume, resume-project, and pause-work reconcile against the versioned scheduler-agnostic manifest stability contract without re-dispatching; the producer is the capability half (#1164). Closes #1165.

scripts/lint-test-file-count.allowlist.json

@@ -168,6 +168,12 @@
         "federated-config-key-removal.test.cjs"
       ],
       "issue": "TBD"
+    },
+    "external-job": {
+      "files": [
+        "external-job-waiting.test.cjs"
+      ],
+      "issue": "#1165"
     }
   }
 }