refactor(terminology): workplan-first state hub resolver internals (CUST-WP-0055 T05)

Rename open-workplan digest helpers, expose open_workplans alongside legacy
open_workstreams in daily triage digests, and update custodian runtime prompt
prose while preserving wire-compat API paths and query params.

k8s/railiance/21-custodian-runtime.yaml

@@ -66,7 +66,7 @@ data:
 
     Optional enrichment:
 
-    - `GET /tasks/?workstream_id=<id>` for a top-ranked workstream
+    - `GET /tasks/?workplan_id=<id>` for a top-ranked workplan (legacy alias: workstream_id)
     - `GET /progress/?workstream_id=<id>&limit=5` for staleness confidence
     - State Hub domain summaries through MCP when available
 
@@ -74,11 +74,11 @@ data:
 
     Build the candidate list from:
 
-    - all open workstreams in `state_summary.open_workstreams`
+    - all open workplans in `state_summary.open_workstreams` (legacy summary key)
     - all derived `state_summary.next_steps`
     - blocked tasks and blocking decisions from the summary
     - high-priority file-backed workplans surfaced by `workplan-index`
-    - workstreams with suspicious structure, such as zero parsed tasks or stale
+    - workplans with suspicious structure, such as zero parsed tasks or stale
       active plans
 
     Keep the scored table compact. Score at most 15 candidates internally and