feat: [finance] 계정과목 및 일반전표 API 추가

- AccountCode 모델/서비스/컨트롤러 구현
- JournalEntry, JournalEntryLine 모델 구현
- GeneralJournalEntry 서비스/컨트롤러 구현
- FormRequest 검증 클래스 추가
- finance 라우트 등록
- i18n 메시지 키 추가 (message.php, error.php)

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

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

@@ -0,0 +1,60 @@
+<?php
+
+namespace App\Http\Controllers\Api\V1;
+
+use App\Helpers\ApiResponse;
+use App\Http\Controllers\Controller;
+use App\Http\Requests\V1\AccountSubject\StoreAccountSubjectRequest;
+use App\Services\AccountCodeService;
+use Illuminate\Http\Request;
+
+class AccountSubjectController extends Controller
+{
+    public function __construct(
+        private readonly AccountCodeService $service
+    ) {}
+
+    /**
+     * 계정과목 목록 조회
+     */
+    public function index(Request $request)
+    {
+        $params = $request->only(['search', 'category']);
+
+        $subjects = $this->service->index($params);
+
+        return ApiResponse::success($subjects, __('message.fetched'));
+    }
+
+    /**
+     * 계정과목 등록
+     */
+    public function store(StoreAccountSubjectRequest $request)
+    {
+        $subject = $this->service->store($request->validated());
+
+        return ApiResponse::success($subject, __('message.created'), [], 201);
+    }
+
+    /**
+     * 계정과목 활성/비활성 토글
+     */
+    public function toggleStatus(int $id, Request $request)
+    {
+        $isActive = (bool) $request->input('is_active', true);
+
+        $subject = $this->service->toggleStatus($id, $isActive);
+
+        return ApiResponse::success($subject, __('message.toggled'));
+    }
+
+    /**
+     * 계정과목 삭제
+     */
+    public function destroy(int $id)
+    {
+        $this->service->destroy($id);
+
+        return ApiResponse::success(null, __('message.deleted'));
+    }
+}