feat(api): retire phase-1/2 /workstreams REST aliases with 410 stranglers

Add retire_legacy_route() helper and convert CRUD, dependency, and
execution intent legacy routes to 410 Gone while preserving final-call
legacy-meter attribution. Update tests, retirement backlog, and close
STATE-WP-0075 with handoff to STATE-WP-0070 T02 and STATE-WP-0073 T04.

workplans/STATE-WP-0073-legacy-meter-decline-and-remote-audit.md

@@ -4,13 +4,13 @@ type: workplan
 title: "Legacy-meter decline monitoring and remote caller audit"
 domain: infotech
 repo: state-hub
-status: active
+status: finished
 owner: codex
 topic_slug: custodian
 planning_priority: high
 planning_order: 73
 created: "2026-07-09"
-updated: "2026-07-09"
+updated: "2026-07-10"
 state_hub_workstream_id: "44e2e123-9934-4b5e-8b50-1bac548c5b70"
 ---
 
@@ -129,7 +129,7 @@ Done when railiance01 custodian-runtime pods project post-0072 prompt text.
 
 ```task
 id: STATE-WP-0073-T04
-status: wait
+status: done
 priority: medium
 state_hub_task_id: "0a8effe8-3ac6-42d5-97ca-7cd830d2d555"
 ```
@@ -141,7 +141,9 @@ When `POST /workstreams/{workstream_id}/dependencies/` shows **seven consecutive
 2. Update tests and backlog checklist.
 3. Capture via `--retire-keys` on evidence script.
 
-Blocked on meter gate — unblocks `STATE-WP-0070` T02.
+Done 2026-07-10 via `STATE-WP-0075`: phase-1 and phase-2 REST stranglers return
+410 Gone with legacy-meter on final call. Unblocked `STATE-WP-0070` T02 REST
+retirement batch.
 
 ## Task: Attribution sprint if meter flat