fix(admin-service): 修复移动端维护状态API响应格式不匹配问题

移动端期望的格式:
{
  "isUnderMaintenance": true,
  "maintenance": { "title", "message", "startTime", "endTime", "remainingMinutes" }
}

后端之前返回的格式:
{
  "inMaintenance": true,
  "title", "message", "endTime"
}

修改内容:
- 字段名 inMaintenance → isUnderMaintenance
- 嵌套维护详情到 maintenance 对象
- 添加 startTime 和 remainingMinutes 字段

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/services/admin-service/src/api/controllers/system-maintenance.controller.ts

@@ -210,14 +210,24 @@ export class MobileMaintenanceController {
     const active = await this.maintenanceRepo.findActiveMaintenance();
 
     if (!active) {
-      return { inMaintenance: false };
+      return { isUnderMaintenance: false, maintenance: null };
     }
 
+    // 计算剩余分钟数
+    const now = new Date();
+    const endTime = new Date(active.endTime);
+    const remainingMs = endTime.getTime() - now.getTime();
+    const remainingMinutes = Math.max(0, Math.ceil(remainingMs / 60000));
+
     return {
-      inMaintenance: true,
-      title: active.title,
-      message: active.message,
-      endTime: active.endTime,
+      isUnderMaintenance: true,
+      maintenance: {
+        title: active.title,
+        message: active.message,
+        startTime: active.startTime,
+        endTime: active.endTime,
+        remainingMinutes,
+      },
     };
   }
 }

backend/services/admin-service/src/api/dto/response/system-maintenance.dto.ts

@@ -66,19 +66,33 @@ export class MaintenanceListResponseDto {
   total: number;
 }
 
+/**
+ * 维护详情（嵌套在状态响应中）
+ */
+export class MaintenanceDetailDto {
+  @ApiProperty({ description: '维护标题' })
+  title: string;
+
+  @ApiProperty({ description: '维护说明' })
+  message: string;
+
+  @ApiProperty({ description: '开始时间' })
+  startTime: Date;
+
+  @ApiProperty({ description: '预计结束时间' })
+  endTime: Date;
+
+  @ApiProperty({ description: '预计剩余分钟数' })
+  remainingMinutes: number;
+}
+
 /**
  * 维护状态响应（给移动端，无需登录）
  */
 export class MaintenanceStatusResponseDto {
   @ApiProperty({ description: '是否在维护中' })
-  inMaintenance: boolean;
+  isUnderMaintenance: boolean;
 
-  @ApiPropertyOptional({ description: '维护标题' })
-  title?: string;
-
-  @ApiPropertyOptional({ description: '维护说明' })
-  message?: string;
-
-  @ApiPropertyOptional({ description: '预计结束时间' })
-  endTime?: Date;
+  @ApiPropertyOptional({ description: '维护详情', type: MaintenanceDetailDto })
+  maintenance?: MaintenanceDetailDto | null;
 }