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/FUNCTIONAL.md

@@ -110,5 +110,15 @@ wins, losses, draws, max points in a game, and max points for a single move (the
 best play, which already includes every word it formed plus the all-tiles bonus).
 
 ### Administration *(Stage 10)*
-Admin (Basic Auth at the gateway) reviews word complaints, manages dictionary
-versions, and inspects users/games.
+Operators reach a server-rendered admin console at `${DOMAIN}/_gm` — the backend
+renders it; the gateway gates it with HTTP Basic Auth on its public listener and
+proxies it verbatim. The console lists and inspects **users** (profile, statistics,
+identities, their games) and **games** (summary + seats), works the **word-complaint
+review queue** — resolving each as reject / accept-add / accept-remove — and exposes
+the **dictionary**: the resident versions per variant, a **hot-reload** of a new
+version from `BACKEND_DICT_DIR/<version>/`, and the **pending wordlist changes**
+derived from accepted complaints (which feed the offline rebuild and are marked
+applied after a reload). When a Telegram connector is configured an operator can also
+**message a user** (by their Telegram identity) or **post to the game channel**.
+State-changing actions are protected by a same-origin check; the console tracks no
+operator identity.