feat: track upstream request ID and prevent response header override

When proxying through another new-api instance, the upstream
X-Oneapi-Request-Id was overwriting the local one in client responses.
This adds a new `upstream_request_id` field to the logs table, captures
the upstream ID during relay, and filters it from being copied back to
the client. Frontend gains search/filter and detail display support.

relay/channel/api_request.go

@@ -524,6 +524,10 @@ func doRequest(c *gin.Context, req *http.Request, info *common.RelayInfo) (*http
 		return nil, errors.New("resp is nil")
 	}
 
+	if upID := resp.Header.Get(common2.RequestIdKey); upID != "" {
+		c.Set(common2.UpstreamRequestIdKey, upID)
+	}
+
 	_ = req.Body.Close()
 	_ = c.Request.Body.Close()
 	return resp, nil