Prod: new admin on admin.*, old admin moves to admin.*/old/

Dockerfile builds apps/backoffice into /srv/admin and the old admin with
base /old/; nginx serves /old/ with its own uncached index.html.
Worker notification links point to the new admin pages (moves, requests,
chats); BACKOFFICE_URL defaults to ADMIN_URL.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

apps/admin/vite.config.ts

@@ -2,7 +2,9 @@ import react from '@vitejs/plugin-react';
 import { defineConfig } from 'vite';
 
 // В разработке API проксируется — Mini App и API на одном origin (удобно и для туннеля https)
+// ADMIN_BASE=/old/ — в продакшене старая админка живёт по адресу admin.barevclub.com/old/
 export default defineConfig({
+  base: process.env.ADMIN_BASE ?? '/',
   plugins: [react()],
   server: {
     host: true,