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/users.gohtml

@@ -0,0 +1,26 @@
+{{define "content" -}}
+<h1>Users</h1>
+{{with .Data}}
+<table class="list">
+<thead><tr><th>Account</th><th>Display name</th><th>Kind</th><th>Lang</th><th>Created</th></tr></thead>
+<tbody>
+{{range .Items}}
+<tr>
+<td><a href="/_gm/users/{{.ID}}">{{.ID}}</a></td>
+<td>{{.DisplayName}}{{if .Guest}} <span class="pill">guest</span>{{end}}</td>
+<td>{{.Kind}}</td>
+<td>{{.Language}}</td>
+<td>{{.CreatedAt}}</td>
+</tr>
+{{else}}
+<tr><td colspan="5"><span class="note">no users</span></td></tr>
+{{end}}
+</tbody>
+</table>
+<nav class="pager">
+{{if .Pager.HasPrev}}<a href="/_gm/users?page={{.Pager.PrevPage}}">&laquo; prev</a>{{end}}
+<span>page {{.Pager.Page}} · {{.Pager.Total}} total</span>
+{{if .Pager.HasNext}}<a href="/_gm/users?page={{.Pager.NextPage}}">next &raquo;</a>{{end}}
+</nav>
+{{end}}
+{{- end}}