feat: Phase 6.1 악성채권 추심관리 API 구현

- 테이블 3개: bad_debts, bad_debt_documents, bad_debt_memos
- 모델 3개: BadDebt, BadDebtDocument, BadDebtMemo
- BadDebtService: CRUD, 요약 통계, 서류/메모 관리
- API 엔드포인트 11개 (목록, 등록, 상세, 수정, 삭제, 토글, 서류/메모 CRUD)
- Swagger 문서 작성 완료

database/migrations/2025_12_19_160001_create_bad_debts_table.php

@@ -0,0 +1,47 @@
+<?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::create('bad_debts', function (Blueprint $table) {
+            $table->id();
+            $table->unsignedBigInteger('tenant_id')->comment('테넌트 ID');
+            $table->unsignedBigInteger('client_id')->comment('거래처 ID');
+            $table->decimal('debt_amount', 15, 2)->default(0)->comment('채권 금액');
+            $table->string('status', 20)->default('collecting')->comment('상태: collecting(추심중), legal_action(법적조치), recovered(회수완료), bad_debt(대손처리)');
+            $table->integer('overdue_days')->default(0)->comment('연체일수');
+            $table->unsignedBigInteger('assigned_user_id')->nullable()->comment('담당자 ID');
+            $table->date('occurred_at')->nullable()->comment('악성채권 발생일');
+            $table->date('closed_at')->nullable()->comment('악성채권 종료일');
+            $table->boolean('is_active')->default(true)->comment('설정 활성화 여부');
+            $table->json('options')->nullable()->comment('추가 옵션 JSON');
+            $table->unsignedBigInteger('created_by')->nullable()->comment('생성자 ID');
+            $table->unsignedBigInteger('updated_by')->nullable()->comment('수정자 ID');
+            $table->unsignedBigInteger('deleted_by')->nullable()->comment('삭제자 ID');
+            $table->timestamps();
+            $table->softDeletes();
+
+            $table->index('tenant_id');
+            $table->index('client_id');
+            $table->index('status');
+            $table->index('is_active');
+            $table->index(['tenant_id', 'status']);
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('bad_debts');
+    }
+};

database/migrations/2025_12_19_160002_create_bad_debt_documents_table.php

@@ -0,0 +1,38 @@
+<?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::create('bad_debt_documents', function (Blueprint $table) {
+            $table->id();
+            $table->unsignedBigInteger('bad_debt_id')->comment('악성채권 ID');
+            $table->string('document_type', 50)->comment('서류 유형: business_license(사업자등록증), tax_invoice(세금계산서), additional(추가서류)');
+            $table->unsignedBigInteger('file_id')->comment('파일 ID');
+            $table->timestamps();
+
+            $table->index('bad_debt_id');
+            $table->index('document_type');
+
+            $table->foreign('bad_debt_id')
+                ->references('id')
+                ->on('bad_debts')
+                ->onDelete('cascade');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('bad_debt_documents');
+    }
+};

database/migrations/2025_12_19_160003_create_bad_debt_memos_table.php

@@ -0,0 +1,37 @@
+<?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::create('bad_debt_memos', function (Blueprint $table) {
+            $table->id();
+            $table->unsignedBigInteger('bad_debt_id')->comment('악성채권 ID');
+            $table->text('content')->comment('메모 내용');
+            $table->unsignedBigInteger('created_by')->nullable()->comment('작성자 ID');
+            $table->timestamps();
+
+            $table->index('bad_debt_id');
+
+            $table->foreign('bad_debt_id')
+                ->references('id')
+                ->on('bad_debts')
+                ->onDelete('cascade');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('bad_debt_memos');
+    }
+};