feat: I-2 거래처 원장 API 구현

- VendorLedgerController: 거래처별 원장 조회 API
- VendorLedgerService: 원장 조회 비즈니스 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/VendorLedgerController.php

@@ -0,0 +1,65 @@
+<?php
+
+namespace App\Http\Controllers\Api\V1;
+
+use App\Helpers\ApiResponse;
+use App\Http\Controllers\Controller;
+use App\Services\VendorLedgerService;
+use Illuminate\Http\Request;
+
+class VendorLedgerController extends Controller
+{
+    public function __construct(
+        private readonly VendorLedgerService $service
+    ) {}
+
+    /**
+     * 거래처원장 목록 (거래처별 매출/수금 집계)
+     */
+    public function index(Request $request)
+    {
+        $params = $request->only([
+            'search',
+            'start_date',
+            'end_date',
+            'sort_by',
+            'sort_dir',
+            'per_page',
+            'page',
+        ]);
+
+        $ledger = $this->service->index($params);
+
+        return ApiResponse::success($ledger, __('message.fetched'));
+    }
+
+    /**
+     * 거래처원장 요약 통계
+     */
+    public function summary(Request $request)
+    {
+        $params = $request->only([
+            'start_date',
+            'end_date',
+        ]);
+
+        $summary = $this->service->summary($params);
+
+        return ApiResponse::success($summary, __('message.fetched'));
+    }
+
+    /**
+     * 거래처원장 상세 (거래처별 거래 내역)
+     */
+    public function show(int $clientId, Request $request)
+    {
+        $params = $request->only([
+            'start_date',
+            'end_date',
+        ]);
+
+        $detail = $this->service->show($clientId, $params);
+
+        return ApiResponse::success($detail, __('message.fetched'));
+    }
+}