feat:E-Sign 전자계약 서명 솔루션 백엔드 구현

- 마이그레이션 4개 (esign_contracts, esign_signers, esign_sign_fields, esign_audit_logs)
- 모델 4개 (EsignContract, EsignSigner, EsignSignField, EsignAuditLog)
- 서비스 4개 (EsignContractService, EsignSignService, EsignPdfService, EsignAuditService)
- 컨트롤러 2개 (EsignContractController, EsignSignController)
- FormRequest 4개 (ContractStore, FieldConfigure, SignSubmit, SignReject)
- Mail 1개 (EsignRequestMail + 이메일 템플릿)
- API 라우트 (인증 계약 관리 + 토큰 기반 서명 프로세스)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/Http/Controllers/Api/V1/ESign/EsignSignController.php

@@ -0,0 +1,75 @@
+<?php
+
+namespace App\Http\Controllers\Api\V1\ESign;
+
+use App\Helpers\ApiResponse;
+use App\Http\Controllers\Controller;
+use App\Http\Requests\ESign\SignRejectRequest;
+use App\Http\Requests\ESign\SignSubmitRequest;
+use App\Services\ESign\EsignSignService;
+use Illuminate\Http\JsonResponse;
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\Storage;
+
+class EsignSignController extends Controller
+{
+    public function __construct(
+        private EsignSignService $service,
+    ) {}
+
+    public function getContract(string $token): JsonResponse
+    {
+        return ApiResponse::handle(function () use ($token) {
+            return $this->service->getByToken($token);
+        }, __('message.fetched'));
+    }
+
+    public function sendOtp(string $token): JsonResponse
+    {
+        return ApiResponse::handle(function () use ($token) {
+            return $this->service->sendOtp($token);
+        }, __('message.esign.otp_sent'));
+    }
+
+    public function verifyOtp(string $token, Request $request): JsonResponse
+    {
+        return ApiResponse::handle(function () use ($token, $request) {
+            $request->validate(['otp_code' => 'required|string|size:6']);
+
+            return $this->service->verifyOtp($token, $request->input('otp_code'));
+        }, __('message.esign.otp_verified'));
+    }
+
+    public function getDocument(string $token): \Symfony\Component\HttpFoundation\StreamedResponse|JsonResponse
+    {
+        try {
+            $data = $this->service->getByToken($token);
+            $contract = $data['contract'];
+            $filePath = $contract->original_file_path;
+
+            if (! $filePath || ! Storage::disk('local')->exists($filePath)) {
+                return ApiResponse::error(__('error.esign.file_not_found'), 404);
+            }
+
+            return Storage::disk('local')->response($filePath, null, [
+                'Content-Type' => 'application/pdf',
+            ]);
+        } catch (\Throwable $e) {
+            return ApiResponse::error($e->getMessage(), $e->getCode() ?: 500);
+        }
+    }
+
+    public function submit(string $token, SignSubmitRequest $request): JsonResponse
+    {
+        return ApiResponse::handle(function () use ($token, $request) {
+            return $this->service->submitSignature($token, $request->validated());
+        }, __('message.esign.signed'));
+    }
+
+    public function reject(string $token, SignRejectRequest $request): JsonResponse
+    {
+        return ApiResponse::handle(function () use ($token, $request) {
+            return $this->service->reject($token, $request->validated()['reason']);
+        }, __('message.esign.rejected'));
+    }
+}