feat(STATE-WP-0079): retire the suggestion-backlog surface (slice E1)

History is archived fleet-side, so the read surface has no remaining job.

- api/routers/suggestions.py: whole prefix 410s with a pointer to intake and
  to the archive; the router drops from 176 lines to a stub
- mcp_server: the 6 suggestion tools removed outright rather than stubbed --
  a retired tool that still appears in the tool list costs every agent
  session context on every call, which is the opposite of retiring it
- write_idempotency: 5 /suggestions rules dropped
- dashboard: suggestions.md deleted, nav entry removed, reference.md and
  wsjf-triage.md updated; docs/suggestions.md rewritten as archive pointer
- tests: two tests pinned the old read-live behaviour and now pin the
  retirement contract instead

Tables stay: they are retire/archive in SHR-INV-0001 and are captured by the
final dump at T06.

Untouched, and worth knowing during cutover: ui-feedback.md / todo.md
'suggestions' are Shift+click dashboard feedback backed by technical_debt, a
different entity that shares the word. E3 (dashboard-meta) is that page; its
owner is state-hub-until-cutover so it retires at the T06 window, not now.

Full suite 612 passed.

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

workplans/STATE-WP-0079-retirement-strangler.md

@@ -184,10 +184,21 @@ notes, 5 bumps, all `declined` in the 2026-07-21 intake migration, none
 promoted. Mutations already 410 since `CUST-WP-0061-T06`; reads were open only
 to keep that history reachable, which the archive now replaces.
 
-E1's remaining removal (8 read routes, 6 MCP tools, 3 tables) is **coupled to
-the dashboard** — `dashboard/src/suggestions.md` is live and referenced from
-`index.md` and `wsjf-triage.md`. The inventory's 17-item count does not show
-this. Sequence with the UI slices A4/B5, not ahead of them.
+**E1 removal executed the same day:** the 8 read routes 410 with a pointer to
+intake and the archive, the 6 MCP tools are removed outright, the 5
+`/suggestions` write-idempotency rules are dropped, and the dashboard page is
+deleted with nav, `reference.md` and `wsjf-triage.md` updated;
+`dashboard/src/docs/suggestions.md` is now the archive pointer. Tables remain
+for the T06 dump. Two tests that pinned the old read-live behaviour were
+rewritten to pin the retirement contract.
+
+Naming trap for cutover: `ui-feedback.md` / `todo.md` "suggestions" are
+Shift+click dashboard feedback backed by `technical_debt`, **not** this
+capability. Untouched.
+
+**E3 (`dashboard-meta`) is `/ui-feedback`** — that same feedback surface. Owner
+is `state-hub-until-cutover` and it is still in use, so it retires at the T06
+freeze window, not now.
 
 Then `dashboard-meta` (E3, 1); `legacy-meter` itself (E4, 9) retires last,
 being the instrument.