Stage 10: admin console & dictionary ops (complaint review, hot-reload, broadcasts)

Server-rendered admin console in the backend at /_gm (internal/adminconsole),
fronted on the gateway's public listener by Basic-Auth + a verbatim reverse proxy
(mounted on the edge mux below the h2c wrap). A same-origin check guards its POSTs;
no operator identity is tracked. This supersedes the Stage 6 gateway-fronts-
/api/v1/admin model: GATEWAY_ADMIN_ADDR and the backend /api/v1/admin ping are
dropped and gateway/internal/admin is repurposed to the verbatim proxy.

- Complaints: migration 00008 (+ jetgen) adds disposition/resolution_note/
  resolved_at/applied_in_version + the deferred status CHECK; resolution feeds a
  query-derived pending dictionary-change pipeline (marked applied after a reload).
- Dictionary hot-reload: per-version subdir BACKEND_DICT_DIR/<version>/ via the new
  Registry.LoadAvailable; engine.OpenWithVersions restores resident versions on
  restart. Partially addresses TODO-2.
- Broadcasts: a backend Telegram-connector client (internal/connector,
  BACKEND_CONNECTOR_ADDR) for SendToUser / SendToGameChannel (discharges the Stage 9
  forward-note).
- Admin reads: account.ListAccounts/CountAccounts/Identities and
  game.ListGames/CountGames/GameByID/ListComplaints/GetComplaint/CountComplaints/
  ResolveComplaint/DictionaryChanges/MarkChangesApplied.
- Tests: adminconsole render, engine reload, same-origin guard, gateway verbatim
  proxy + h2c console mount, inttest complaint pipeline + list/count + /_gm console.
- Docs: PLAN (Stage 10 done + refinements + TODO-2), ARCHITECTURE §1/§5/§6/§12/§13,
  FUNCTIONAL (+_ru), TESTING, backend/gateway READMEs.

docs/TESTING.md

@@ -82,6 +82,17 @@ tests or touching CI.
   in `inttest`. Stage 8 adds gateway transcode round-trips for the new social/account
   operations (friends list, friend code issue/redeem, invitation create, stats, GCG,
   the profile-update away round-trip) and a `notify`-event constructor round-trip.
+- **Admin & dictionary ops** *(Stage 10)* — `backend/internal/adminconsole` unit-tests
+  the template renderer over every page plus the embedded asset; `backend/internal/engine`
+  adds the **dictionary hot-reload** cases (`LoadAvailable` loads only the present
+  variants, `OpenWithVersions` scans version subdirectories, a reload registers a new
+  version and moves "latest"); `backend/internal/server` unit-tests the console's
+  **same-origin** CSRF guard; the gateway adds the **verbatim `/_gm` Basic-Auth proxy**
+  (401 / forward, path preserved) and the h2c **console mount** (routed when configured,
+  404 when not). Postgres-backed `inttest` drives the **complaint resolution →
+  dictionary-change pipeline** (file → resolve with a disposition → pending change → mark
+  applied), the admin **list/count** read queries, and the **/_gm console over HTTP**
+  (pages render; a resolve POST needs a same-origin header).
 
 ## Principles