STATE-WP-0072: sync custodian triage prompt to /workplans/index

Align railiance k8s projected prompt with custodian runtime prompt;
drop retired workplan-index legacy path.

k8s/railiance/21-custodian-runtime.yaml

@@ -39,7 +39,7 @@ data:
     - Read first, then decide. Do not edit workplans, canon, or task status during
       a daily review unless a later human request explicitly asks for an apply step.
     - Prefer existing State Hub read surfaces over ad hoc scans:
-      `/state/summary`, `/state/next_steps`, `/workstreams/workplan-index`,
+      `/state/summary`, `/state/next_steps`, `/workplans/index`,
       `/messages/`, and `.custodian-brief.md`.
     - Use local workplan files only to enrich the State Hub snapshot with task
       wording, stale frontmatter, and missing file-backed state.
@@ -60,7 +60,7 @@ data:
     2. `GET http://127.0.0.1:8000/state/summary`
     3. `GET http://127.0.0.1:8000/messages/?to_agent=hub&unread_only=true`
     4. `GET http://127.0.0.1:8000/state/next_steps`
-    5. `GET http://127.0.0.1:8000/workstreams/workplan-index`
+    5. `GET http://127.0.0.1:8000/workplans/index`
     6. Local workplan files for candidate workplans that need closer inspection
     7. Read-only `git status --short` for repos named in top recommendations