feat: [approvals] 결재선 템플릿 CRUD 기능 추가

- POST/PUT/DELETE /api/admin/approvals/lines 라우트 추가
- ApprovalApiController storeLine/updateLine/destroyLine 메서드
- ApprovalService createLine/updateLine/deleteLine + enrichLineSteps 헬퍼
- 기안함 화면에 결재선 관리 버튼 + 모달 UI (목록/편집 2-state)

app/Http/Controllers/Api/Admin/ApprovalApiController.php

@@ -367,6 +367,63 @@ public function lines(): JsonResponse
         return response()->json(['success' => true, 'data' => $lines]);
     }
 
+    /**
+     * 결재선 템플릿 생성
+     */
+    public function storeLine(Request $request): JsonResponse
+    {
+        $request->validate([
+            'name' => 'required|string|max:100',
+            'steps' => 'required|array|min:1',
+            'steps.*.user_id' => 'required|exists:users,id',
+            'steps.*.step_type' => 'required|in:approval,agreement,reference',
+            'is_default' => 'boolean',
+        ]);
+
+        $line = $this->service->createLine($request->all());
+
+        return response()->json([
+            'success' => true,
+            'message' => '결재선이 저장되었습니다.',
+            'data' => $line,
+        ], 201);
+    }
+
+    /**
+     * 결재선 템플릿 수정
+     */
+    public function updateLine(Request $request, int $id): JsonResponse
+    {
+        $request->validate([
+            'name' => 'required|string|max:100',
+            'steps' => 'required|array|min:1',
+            'steps.*.user_id' => 'required|exists:users,id',
+            'steps.*.step_type' => 'required|in:approval,agreement,reference',
+            'is_default' => 'boolean',
+        ]);
+
+        $line = $this->service->updateLine($id, $request->all());
+
+        return response()->json([
+            'success' => true,
+            'message' => '결재선이 수정되었습니다.',
+            'data' => $line,
+        ]);
+    }
+
+    /**
+     * 결재선 템플릿 삭제
+     */
+    public function destroyLine(int $id): JsonResponse
+    {
+        $this->service->deleteLine($id);
+
+        return response()->json([
+            'success' => true,
+            'message' => '결재선이 삭제되었습니다.',
+        ]);
+    }
+
     /**
      * 양식 목록
      */