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.

backend/internal/adminconsole/templates/pages/dashboard.gohtml

@@ -0,0 +1,24 @@
+{{define "content" -}}
+<h1>Dashboard</h1>
+<p class="lede">Operator console for users, games, complaints and dictionaries.</p>
+{{with .Data}}
+<div class="cards">
+<a class="card" href="/_gm/users"><h2>Users</h2><p class="bignum">{{.Accounts}}</p></a>
+<a class="card" href="/_gm/games"><h2>Games</h2><p class="bignum">{{.Games}}</p></a>
+<a class="card" href="/_gm/games?status=active"><h2>Active games</h2><p class="bignum">{{.ActiveGames}}</p></a>
+<a class="card" href="/_gm/complaints?status=open"><h2>Open complaints</h2><p class="bignum">{{.OpenComplaints}}</p></a>
+<a class="card" href="/_gm/dictionary"><h2>Pending dict changes</h2><p class="bignum">{{.PendingChanges}}</p></a>
+</div>
+<section class="panel">
+<h2>Dictionaries</h2>
+<table class="list">
+<thead><tr><th>Variant</th><th>Latest</th><th>Resident versions</th></tr></thead>
+<tbody>
+{{range .Variants}}
+<tr><td>{{.Variant}}</td><td>{{.Latest}}</td><td>{{range .Versions}}<span class="pill">{{.}}</span> {{end}}</td></tr>
+{{end}}
+</tbody>
+</table>
+</section>
+{{end}}
+{{- end}}