fix: Guard against undefined stats in AdminDashboard formatValue

API returns partial/empty stats object — individual fields can be undefined
even when the object exists. Added null guard to prevent toLocaleString crash.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/views/platform-admin/AdminDashboard.vue

@@ -35,7 +35,8 @@ const quickLinks = [
   { label: 'Servers', description: 'Monitor connected game servers', icon: MonitorCog, route: '/platform-admin/servers' },
 ]
 
-function formatValue(value: number, format: string): string {
+function formatValue(value: number | undefined, format: string): string {
+  if (value == null) return '\u2014'
   if (format === 'currency') {
     return `$${value.toFixed(2)}`
   }