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/openai/audio.go

@@ -30,6 +30,9 @@ func OpenaiTTSHandler(c *gin.Context, resp *http.Response, info *relaycommon.Rel
 	usage.PromptTokens = info.GetEstimatePromptTokens()
 	usage.TotalTokens = info.GetEstimatePromptTokens()
 	for k, v := range resp.Header {
+		if !service.ShouldCopyUpstreamHeader(c, k, v) {
+			continue
+		}
 		c.Writer.Header().Set(k, v[0])
 	}
 	c.Writer.WriteHeader(resp.StatusCode)