fix(platform): 公开既有账号文件容量上限 (#684)

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

backend/internal/platform/runtime_policy.go

@@ -137,6 +137,7 @@ type PublicRuntimePolicySetting struct {
 type PublicRuntimeLimits struct {
 	ActiveTaskLimit         int   `json:"activeTaskLimit"`
 	ResourceUploadMB        int64 `json:"resourceUploadMB"`
+	StoredFileGB            int64 `json:"storedFileGB"`
 	RecycleBinRetentionDays int   `json:"recycleBinRetentionDays"`
 }
 
@@ -274,6 +275,7 @@ func (s *Service) PublicRuntimeLimits() (*PublicRuntimeLimits, error) {
 	}
 	return &PublicRuntimeLimits{
 		ActiveTaskLimit: policy.Task.ActiveTaskLimit, ResourceUploadMB: policy.Resource.ResourceUploadMB,
+		StoredFileGB:            policy.Resource.StoredFileGB,
 		RecycleBinRetentionDays: policy.Resource.RecycleBinRetentionDays,
 	}, nil
 }