feat: add system info card to admin dashboard

Shows cabinet version, bot version, Python version, uptime, users and
active subscriptions at the bottom of the dashboard page.

vite.config.ts

@@ -1,10 +1,14 @@
 import { defineConfig } from 'vite';
 import react from '@vitejs/plugin-react';
 import path from 'path';
+import packageJson from './package.json';
 
 // https://vitejs.dev/config/
 export default defineConfig({
   plugins: [react()],
+  define: {
+    __APP_VERSION__: JSON.stringify(packageJson.version),
+  },
   resolve: {
     alias: {
       '@': path.resolve(__dirname, 'src'),