feat: [calendar,vat] 캘린더 CRUD 및 부가세 상세 조회 API 추가

- CalendarController/Service: 일정 등록/수정/삭제 API 추가
- VatController/Service: getDetail() 상세 조회 (요약, 참조테이블, 미발행 목록, 신고기간 옵션)
- 라우트: POST/PUT/DELETE /calendar/schedules, GET /vat/detail 추가

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

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

@@ -32,4 +32,18 @@ public function summary(Request $request): JsonResponse
             return $this->vatService->getSummary($periodType, $year, $period);
         }, __('message.fetched'));
     }
+
+    /**
+     * 부가세 상세 조회 (모달용)
+     */
+    public function detail(Request $request): JsonResponse
+    {
+        $periodType = $request->query('period_type', 'quarter');
+        $year = $request->query('year') ? (int) $request->query('year') : null;
+        $period = $request->query('period') ? (int) $request->query('period') : null;
+
+        return ApiResponse::handle(function () use ($periodType, $year, $period) {
+            return $this->vatService->getDetail($periodType, $year, $period);
+        }, __('message.fetched'));
+    }
 }