feat: I-5 미수금 현황 API 구현

- ReceivablesController: 미수금 조회 API
- ReceivablesService: 미수금 조회 로직
- Swagger 문서화

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/Http/Controllers/Api/V1/ReceivablesController.php

@@ -0,0 +1,49 @@
+<?php
+
+namespace App\Http\Controllers\Api\V1;
+
+use App\Helpers\ApiResponse;
+use App\Http\Controllers\Controller;
+use App\Services\ReceivablesService;
+use Illuminate\Http\JsonResponse;
+use Illuminate\Http\Request;
+
+/**
+ * 채권 현황 컨트롤러
+ */
+class ReceivablesController extends Controller
+{
+    public function __construct(
+        protected ReceivablesService $service
+    ) {}
+
+    /**
+     * 채권 현황 목록 조회
+     */
+    public function index(Request $request): JsonResponse
+    {
+        return ApiResponse::handle(function () use ($request) {
+            $params = $request->validate([
+                'year' => 'nullable|integer|min:2000|max:2100',
+                'search' => 'nullable|string|max:100',
+                'has_receivable' => 'nullable|boolean',
+            ]);
+
+            return $this->service->index($params);
+        }, __('message.fetched'));
+    }
+
+    /**
+     * 채권 현황 요약 통계
+     */
+    public function summary(Request $request): JsonResponse
+    {
+        return ApiResponse::handle(function () use ($request) {
+            $params = $request->validate([
+                'year' => 'nullable|integer|min:2000|max:2100',
+            ]);
+
+            return $this->service->summary($params);
+        }, __('message.fetched'));
+    }
+}