Hub stage 5: manage each server from one console

Zones, Cache, Blocking, DNS Client, Settings, DHCP and Logs can now be
changed on one chosen server through the hub, with that server's admin
token. Operators manage cache and blocking; admins also zones, settings
and DHCP. Under "All servers", or on a server without an admin token,
the controls are disabled with a hint.

The hub refuses settings/set changes to a server's web service fields
and anything about users, SSO or LDAP; backup, restore, log and stats
deletion and admin/* stay refused. Non-admins get settings with secrets
blanked. Write params travel in the POST body, downloads pass through
with a single-use token, and the audit log names no values.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/compose.hub.example.yaml

@@ -11,7 +11,7 @@ version: "3.8"
 # Токены кладутся в .env рядом с этим файлом (не в git):
 #   MDNS_TOKEN=...
 #   NDNS_TOKEN=...
-#   MDNS_ADMIN_TOKEN=...   # токены hub-admin (Modify и Delete только на Apps): нужны, чтобы хаб менял приложения
+#   MDNS_ADMIN_TOKEN=...   # токены hub-admin (Modify и Delete только в разделах, которыми управляете из хаба, см. docs/hub-deploy.md): нужны, чтобы хаб менял приложения и серверы
 #   NDNS_ADMIN_TOKEN=...
 #   HUB_USER=...        # логин в сам хаб
 #   HUB_PASSWORD=...    # первый вход; затем пользователи в /data/users.json (docs/hub-deploy.md, шаг 4a)