Accept non-UUID triggering_event_id and add GitOps runbook

Broaden POST /issues/ so triggering_event_id is any non-empty traceability
string, enabling cron/scheduled activity-core emissions with stable keys like
"scheduled" while event-driven paths still send UUIDs. Document the railiance01
ArgoCD deployment path in docs/argocd-gitops.md and update ISSUE-WP-0003 task
status to reflect repo-side progress.

SCOPE.md

@@ -135,11 +135,17 @@ user directory.
   "due_in_days": 7,
   "source_type": "rule | instruction",
   "source_id": "string",
-  "triggering_event_id": "uuid",
+  "triggering_event_id": "event uuid or stable source key",
   "activity_definition_id": "string"
 }
 ```
 
+`triggering_event_id` is accepted as a non-empty string. Event-driven
+emissions should send the upstream activity event UUID. Scheduled or cron
+emissions that do not have a concrete event row may send a stable source key
+such as `scheduled`; issue-core stores the value verbatim in ingestion
+metadata for traceability.
+
 ### `POST /issues/` response
 
 ```json