fix(workplans): qualify ad-hoc identifiers with the repository prefix

`ADHOC-YYYY-MM-DD` is unique per date but not per repository, so any two repos
opening an ad-hoc on the same day collide. The 2026-08-26 fleet projection
reset refused 9 records for exactly this reason.

Canon (work-record-types_v0.1, CUST-WP-0066) settled the form as
`{PREFIX}-WP-ADHOC-YYYY-MM-DD`, filename unchanged, and grandfathered existing
ids on the condition they are never *silently* re-derived. This is the explicit
migration that clause allows for.

The hub id is derived from the record id, so a changed id is a different
record: stale state_hub_*_id fields are dropped and fix-consistency re-derives.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

workplans/ADHOC-2026-05-02.md

@@ -1,5 +1,5 @@
 ---
-id: ADHOC-2026-05-02
+id: CUST-WP-ADHOC-2026-05-02
 type: workplan
 title: "Ad Hoc Tasks — 2026-05-02"
 domain: custodian
@@ -9,10 +9,9 @@ owner: custodian
 topic_slug: custodian
 created: "2026-05-02"
 updated: "2026-05-02"
-state_hub_workstream_id: "3f54ce9c-1f95-42de-894f-0f81a52ba2e8"
 ---
 
-# ADHOC-2026-05-02 — Ad Hoc Tasks
+# CUST-WP-ADHOC-2026-05-02 — Ad Hoc Tasks
 
 Small same-day improvements that are useful to track, but do not justify a
 dedicated requirement/workplan cycle.
@@ -20,10 +19,9 @@ dedicated requirement/workplan cycle.
 ## Overview workplans by repository
 
 ```task
-id: ADHOC-2026-05-02-T01
+id: CUST-WP-ADHOC-2026-05-02-T01
 status: done
 priority: medium
-state_hub_task_id: "e9a302b7-81ab-4643-a256-4565a8c753e0"
 ```
 
 Changed the State Hub Overview workplan chart from domain-first grouping to