feat(purchase): 采购申请批量审批（解决循环提交需多次审批）

问题: 一次提交 10 个物品生成 10 条独立申请，审批人需操作 10 次

后端:
- 新增 POST /api/v1/purchase/batch-approve 批量审批接口
  接收 ids + action，循环审批，成功/失败分别返回

前端:
- 待审批列表加多选列（仅 status=0 可勾选）
- 顶部批量操作栏：批量通过 / 批量驳回 / 取消选择
- 批量驳回弹窗统一填写驳回原因

inventory-backend/app/api/v1/purchase.py

@@ -205,6 +205,61 @@ def approve_purchase_request(purchase_id):
 # 5. 获取可选审批人列表
 # GET /api/v1/purchase/approvers
 # --------------------------------------------------------
+@purchase_bp.route('/batch-approve', methods=['POST'])
+@jwt_required()
+@permission_required('inbound_purchase:operation')
+def batch_approve_purchase():
+    """
+    批量审批采购申请（解决循环提交导致的多条记录需多次审批问题）
+
+    请求体:
+    {
+        "ids": [1, 2, 3],
+        "action": "approve" | "reject",
+        "reject_reason": "驳回原因（reject 时必填）"
+    }
+    """
+    try:
+        user_id = get_current_user_id()
+        data = request.get_json() or {}
+        ids = data.get('ids', [])
+        action = data.get('action', 'approve')
+        reject_reason = data.get('reject_reason')
+
+        if not ids or not isinstance(ids, list):
+            return jsonify({'code': 400, 'msg': 'ids 不能为空'}), 400
+        if action not in ('approve', 'reject'):
+            return jsonify({'code': 400, 'msg': '无效的审批操作'}), 400
+        if action == 'reject' and not reject_reason:
+            return jsonify({'code': 400, 'msg': '驳回时必须提供原因'}), 400
+
+        success_ids = []
+        error_items = []
+        for pid in ids:
+            try:
+                purchase = PurchaseService.approve_purchase_request(
+                    purchase_id=pid,
+                    user_id=user_id,
+                    action=action,
+                    reject_reason=reject_reason
+                )
+                success_ids.append(purchase.id)
+            except ValueError as e:
+                error_items.append({'id': pid, 'msg': str(e)})
+            except Exception as e:
+                traceback.print_exc()
+                error_items.append({'id': pid, 'msg': str(e)})
+
+        msg = f'批量审批完成: 成功 {len(success_ids)} 条'
+        if error_items:
+            msg += f', 失败 {len(error_items)} 条'
+        return jsonify({'code': 200, 'msg': msg, 'data': {'success_ids': success_ids, 'errors': error_items}}), 200
+
+    except Exception as e:
+        traceback.print_exc()
+        return jsonify({'code': 500, 'msg': f'服务器内部错误: {str(e)}'}), 500
+
+
 @purchase_bp.route('/approvers', methods=['GET'])
 @jwt_required()
 def get_purchase_approvers():