feat(billing): renewals, coupons, VAT numbering, billing cycles and invoice payment tracking

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

app/Http/Controllers/Api/Admin/EmailTemplate/EmailHealthController.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace App\Http\Controllers\Api\Admin\EmailTemplate;
+
+use App\Http\Controllers\Controller;
+use App\Support\EmailHealth;
+use Illuminate\Http\JsonResponse;
+
+class EmailHealthController extends Controller
+{
+    public function show(): JsonResponse
+    {
+        return response()->json(['error' => false, 'data' => EmailHealth::report()]);
+    }
+}