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/Setting/VatNumberingController.php

@@ -0,0 +1,41 @@
+<?php
+
+namespace App\Http\Controllers\Api\Admin\Setting;
+
+use App\Http\Controllers\Controller;
+use App\Models\Invoice;
+use App\Support\VatSettings;
+use Illuminate\Http\JsonResponse;
+use Illuminate\Http\Request;
+
+class VatNumberingController extends Controller
+{
+    public function show(): JsonResponse
+    {
+        return response()->json(['error' => false, 'data' => VatSettings::numbering()]);
+    }
+
+    public function update(Request $request): JsonResponse
+    {
+        $data = $request->validate([
+            'serial' => 'required|string|max:20|regex:/^[A-Za-z0-9]+$/',
+            'next_number' => 'required|integer|min:1',
+            'padding' => 'required|integer|min:1|max:12',
+            'auto_issue' => 'required|boolean',
+        ]);
+
+        $data['serial'] = strtoupper($data['serial']);
+
+        $lastIssued = Invoice::query()->where('vat_serial', $data['serial'])->whereNotNull('vat_number')->max('vat_number');
+        if ($lastIssued !== null && $data['next_number'] <= (int) $lastIssued) {
+            return response()->json([
+                'error' => true,
+                'message' => "Số tiếp theo phải lớn hơn số đã cấp gần nhất ({$lastIssued}) của ký hiệu {$data['serial']}",
+            ], 422);
+        }
+
+        VatSettings::saveNumbering($data);
+
+        return response()->json(['error' => false, 'message' => 'Đã lưu cấu hình đánh số hóa đơn VAT', 'data' => VatSettings::numbering()]);
+    }
+}