feat: 매입 세금계산서 수취 토글 기능 추가

- Purchase 모델에 tax_invoice_received 필드 추가
- PurchaseService에 toggleTaxInvoice() 메서드 추가
- UpdatePurchaseRequest에 tax_invoice_received 검증 규칙 추가
- 마이그레이션: purchases 테이블에 tax_invoice_received 컬럼 추가

database/migrations/2025_12_24_160000_add_tax_invoice_received_to_purchases_table.php

@@ -0,0 +1,28 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::table('purchases', function (Blueprint $table) {
+            $table->boolean('tax_invoice_received')->default(false)->after('withdrawal_id')->comment('세금계산서 수취 여부');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('purchases', function (Blueprint $table) {
+            $table->dropColumn('tax_invoice_received');
+        });
+    }
+};