Add the admin panel scaffold

A self-contained template: an Express backend with login, JWT, rate limiting
and SPA serving, and a React 18 + Vite shell with the same tab registry and
warm Material 3 design system the panel uses. No domain logic — routes and tabs
are meant to be hung off it.

node_modules and the frontend build stay out through the existing ignores.

admin/frontend/vite.config.ts

@@ -0,0 +1,18 @@
+// Copyright (c) 2026 Ivan Vasilev
+// This source code is licensed under the MIT license found in the
+// LICENSE file in the root directory of this source tree.
+import { defineConfig } from 'vite';
+import react from '@vitejs/plugin-react';
+
+// В деве Vite (:5173) проксирует запросы на бэкенд (:8080) — фронт всегда
+// ходит по относительным путям, порт нигде не зашит.
+export default defineConfig({
+    plugins: [react()],
+    server: {
+        proxy: {
+            '/api':    'http://localhost:8080',
+            '/login':  'http://localhost:8080',
+            '/logout': 'http://localhost:8080',
+        },
+    },
+});