fix(poll): GetPackages 接口新增分页 POLL-03

- 新增 AssetPackagesResult DTO（含 total/page/page_size/items 字段）
- GetPackages 签名新增 page/pageSize 参数，默认 page=1、pageSize=50、最大 100
- admin/asset.go:Packages 从 Query 参数读取 page/page_size 传入 Service
- client_asset.go 调用处同步更新，使用默认分页参数

internal/handler/app/client_asset.go

@@ -210,11 +210,11 @@ func (h *ClientAssetHandler) GetAvailablePackages(c *fiber.Ctx) error {
 		return errors.New(errors.CodeNoAvailablePackage, "当前无可购买套餐")
 	}
 
-	allUsages, err := h.assetService.GetPackages(resolved.SkipPermissionCtx, resolved.Asset.AssetType, resolved.Asset.AssetID)
+	packagesResult, err := h.assetService.GetPackages(resolved.SkipPermissionCtx, resolved.Asset.AssetType, resolved.Asset.AssetID, 1, 50)
 	if err != nil {
 		return err
 	}
-	resolved.MainPackageActived = hasActiveMainPackage(allUsages)
+	resolved.MainPackageActived = hasActiveMainPackage(packagesResult.Items)
 
 	listCtx := resolved.SkipPermissionCtx
 	if resolved.IsAgentChannel {