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/dify/relay-dify.go

@@ -223,33 +223,32 @@ func difyStreamHandler(c *gin.Context, info *relaycommon.RelayInfo, resp *http.R
 	usage := &dto.Usage{}
 	var nodeToken int
 	helper.SetEventStreamHeaders(c)
-	helper.StreamScannerHandler(c, resp, info, func(data string) bool {
+	helper.StreamScannerHandler(c, resp, info, func(data string, sr *helper.StreamResult) {
 		var difyResponse DifyChunkChatCompletionResponse
-		err := json.Unmarshal([]byte(data), &difyResponse)
-		if err != nil {
+		if err := json.Unmarshal([]byte(data), &difyResponse); err != nil {
 			common.SysLog("error unmarshalling stream response: " + err.Error())
-			return true
+			sr.Error(err)
+			return
 		}
-		var openaiResponse dto.ChatCompletionsStreamResponse
 		if difyResponse.Event == "message_end" {
 			usage = &difyResponse.MetaData.Usage
-			return false
+			sr.Done()
+			return
 		} else if difyResponse.Event == "error" {
-			return false
-		} else {
-			openaiResponse = *streamResponseDify2OpenAI(difyResponse)
-			if len(openaiResponse.Choices) != 0 {
-				responseText += openaiResponse.Choices[0].Delta.GetContentString()
-				if openaiResponse.Choices[0].Delta.ReasoningContent != nil {
-					nodeToken += 1
-				}
+			sr.Stop(fmt.Errorf("dify error event"))
+			return
+		}
+		openaiResponse := *streamResponseDify2OpenAI(difyResponse)
+		if len(openaiResponse.Choices) != 0 {
+			responseText += openaiResponse.Choices[0].Delta.GetContentString()
+			if openaiResponse.Choices[0].Delta.ReasoningContent != nil {
+				nodeToken += 1
 			}
 		}
-		err = helper.ObjectData(c, openaiResponse)
-		if err != nil {
+		if err := helper.ObjectData(c, openaiResponse); err != nil {
 			common.SysLog(err.Error())
+			sr.Error(err)
 		}
-		return true
 	})
 	helper.Done(c)
 	if usage.TotalTokens == 0 {