接单平台等级 CRUD 完善，修复默认分类停用被重置

- 等级面板支持编辑、启用/停用切换、删除（默认等级与使用中等级受保护）
- 新增等级删除接口及使用量校验
- 修复默认分类停用后被 ensureWorkerPlatformDefaults 重置为启用的问题，默认分类仅不存在时创建
- 分类操作后改为显式刷新列表

apps/backend/src/services/worker-platform/worker-platform-service.ts

@@ -10,14 +10,17 @@ import {
   countWorkerAcceptedOrders,
   countWorkerActiveOrders,
   countWorkCategoryUsages,
+  countWorkerLevelUsages,
   createWorkOrder,
   createWorkOrderEvent,
   createWorkerFinanceRequest,
   createWorkerUser,
   deleteWorkCategory,
+  deleteWorkerLevel,
   getWorkerFinanceRequestById,
   getWorkerFinanceRequestSummary,
   getWorkCategoryById,
+  getWorkCategoryByKey,
   getWorkerLevelById,
   getWorkerLevelByKey,
   getWorkerUserByInviteCode,
@@ -110,13 +113,16 @@ export async function ensureWorkerPlatformDefaults() {
       }),
       now,
     }))
-  const category = await upsertWorkCategory({
-    categoryKey: DEFAULT_CATEGORY_KEY,
-    name: '默认分类',
-    sortOrder: 100,
-    status: 'active',
-    now,
-  })
+  const existingCategory = await getWorkCategoryByKey(DEFAULT_CATEGORY_KEY)
+  const category =
+    existingCategory ||
+    (await upsertWorkCategory({
+      categoryKey: DEFAULT_CATEGORY_KEY,
+      name: '默认分类',
+      sortOrder: 100,
+      status: 'active',
+      now,
+    }))
   return { level, category }
 }
 
@@ -933,6 +939,31 @@ export async function saveAdminWorkerLevel(payload: JsonObject = {}) {
   return { level: mapWorkerLevel(level) }
 }
 
+export async function deleteAdminWorkerLevel(levelId: number | string) {
+  const level = await getWorkerLevelById(Number(levelId))
+  if (!level) {
+    throw createHttpError('等级不存在', {
+      statusCode: 404,
+      errorCode: 'worker_level_not_found',
+    })
+  }
+  if (level.level_key === DEFAULT_LEVEL_KEY) {
+    throw createHttpError('默认等级（VIP1）不可删除', {
+      statusCode: 409,
+      errorCode: 'worker_level_default_protected',
+    })
+  }
+  const usageCount = await countWorkerLevelUsages(Number(levelId))
+  if (usageCount > 0) {
+    throw createHttpError(`该等级正在被 ${usageCount} 名打手使用，请先调整打手等级后再删除`, {
+      statusCode: 409,
+      errorCode: 'worker_level_in_use',
+    })
+  }
+  const { deleted } = await deleteWorkerLevel(Number(levelId))
+  return { deleted }
+}
+
 export async function listAdminWorkProductRules(query: JsonObject = {}) {
   await ensureWorkerPlatformDefaults()
   const enabledValue = String(query.enabled ?? '').trim()