feat(API): 복리후생비 상세 API 추가 (/welfare/detail)

- WelfareService: getDetail() 메서드 및 헬퍼 메서드 추가
  - getAccountBalance(), getMonthlyUsageTrend()
  - getCategoryDistribution(), getTransactions()
  - getQuarterlyStatus()
- WelfareController: detail() 액션 추가
- routes/api.php: /welfare/detail 라우트 등록
- Swagger: WelfareDetailResponse 및 관련 스키마 7개 추가

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

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

@@ -21,9 +21,6 @@ public function __construct(
 
     /**
      * 복리후생비 현황 요약 조회
-     *
-     * @param  Request  $request
-     * @return JsonResponse
      */
     public function summary(Request $request): JsonResponse
     {
@@ -49,4 +46,30 @@ public function summary(Request $request): JsonResponse
             );
         }, __('message.fetched'));
     }
-}
+
+    /**
+     * 복리후생비 상세 조회 (모달용)
+     */
+    public function detail(Request $request): JsonResponse
+    {
+        $calculationType = $request->query('calculation_type', 'fixed');
+        $fixedAmountPerMonth = $request->query('fixed_amount_per_month')
+            ? (int) $request->query('fixed_amount_per_month')
+            : 200000;
+        $ratio = $request->query('ratio')
+            ? (float) $request->query('ratio')
+            : 0.05;
+        $year = $request->query('year') ? (int) $request->query('year') : null;
+        $quarter = $request->query('quarter') ? (int) $request->query('quarter') : null;
+
+        return ApiResponse::handle(function () use ($calculationType, $fixedAmountPerMonth, $ratio, $year, $quarter) {
+            return $this->welfareService->getDetail(
+                $calculationType,
+                $fixedAmountPerMonth,
+                $ratio,
+                $year,
+                $quarter
+            );
+        }, __('message.fetched'));
+    }
+}