Hide the brand from unauthenticated requests

GET /ui/brand answered without auth with {"brand":"Forgetting",…}: one
request was enough for a scanner to tell a found port is this panel. It now
requires the panel JWT (Go and the Node reference alike). The login screen
says just «Вход», the page title is neutral until login, and the wordmark
loads after sign-in.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013bNGYiDst62wH3ZGTRPFLJ

README.md

@@ -187,7 +187,7 @@ TOKEN=$(curl -s -X POST http://HOST:PORT/login \
 
 | Метод | Ответ |
 |---|---|
-| `GET /ui/brand` | `{ "brand": "Forgetting", "channel": "Beta", "version": "0.4.7" }` — **без авторизации**, панель берёт отсюда вордмарк на экране логина |
+| `GET /ui/brand` | `{ "brand": "Forgetting", "channel": "Beta", "version": "0.4.7" }` — требует JWT панели (без авторизации выдавал бы панель сканерам). Вордмарк в шапке после входа |
 | `GET /health` | `{ "status", "server", "ip", "gen", "awg": { "status", "peers", "module", "tools" } }`. `200`, если интерфейс поднят, иначе `503` и `status: "degraded"` |
 | `GET /awg/status` | `{ "up": true, "peers": 3, "publicKey": "…" }` |