adminAuthGuard only checked isAuthenticated() - any signed-in admin
could reach any route. The live Telegram/QR auth (Mechanism A) carries
no role claim, so a real gate needs a backend change (tracked in
BACKEND-API-REFERENCE.md).
Added AdminPermissionsService + requireAdminPermission() guard factory
that derive a permission set locally by matching the Telegram username
against the mock Users domain's roleId - the same local-only stand-in
already used for the rest of that domain. Wired onto /backoffice/users
requiring 'users.manage'. Explicitly cosmetic: backend must
independently authorize every mutation regardless of what this guard
decides.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>