feat: record stream interruption reasons via StreamStatus

- Add StreamStatus type (relay/common) to track stream end reason
  (done/timeout/client_gone/scanner_error/eof/panic/ping_fail) and
  accumulate soft errors during streaming via sync.Once + sync.Mutex.
- Add StreamResult (relay/helper) as the callback interface: adapters
  call sr.Error() for soft errors, sr.Stop() for fatal, sr.Done() for
  normal completion. No early-return problem — multiple errors per chunk
  are naturally supported.
- Refactor StreamScannerHandler callback from func(string) bool to
  func(string, *StreamResult). All 9 channel adapters updated.
- Write stream_status into log other JSON field (admin-only) with
  status ok/error, end_reason, error_count, and error messages.
- Frontend: display stream status in log detail expansion for admins.

relay/channel/baidu/relay-baidu.go

@@ -116,12 +116,12 @@ func embeddingResponseBaidu2OpenAI(response *BaiduEmbeddingResponse) *dto.OpenAI
 
 func baiduStreamHandler(c *gin.Context, info *relaycommon.RelayInfo, resp *http.Response) (*types.NewAPIError, *dto.Usage) {
 	usage := &dto.Usage{}
-	helper.StreamScannerHandler(c, resp, info, func(data string) bool {
+	helper.StreamScannerHandler(c, resp, info, func(data string, sr *helper.StreamResult) {
 		var baiduResponse BaiduChatStreamResponse
-		err := common.Unmarshal([]byte(data), &baiduResponse)
-		if err != nil {
+		if err := common.Unmarshal([]byte(data), &baiduResponse); err != nil {
 			common.SysLog("error unmarshalling stream response: " + err.Error())
-			return true
+			sr.Error(err)
+			return
 		}
 		if baiduResponse.Usage.TotalTokens != 0 {
 			usage.TotalTokens = baiduResponse.Usage.TotalTokens
@@ -129,11 +129,10 @@ func baiduStreamHandler(c *gin.Context, info *relaycommon.RelayInfo, resp *http.
 			usage.CompletionTokens = baiduResponse.Usage.TotalTokens - baiduResponse.Usage.PromptTokens
 		}
 		response := streamResponseBaidu2OpenAI(&baiduResponse)
-		err = helper.ObjectData(c, response)
-		if err != nil {
+		if err := helper.ObjectData(c, response); err != nil {
 			common.SysLog("error sending stream response: " + err.Error())
+			sr.Error(err)
 		}
-		return true
 	})
 	service.CloseResponseBodyGracefully(resp)
 	return nil, usage