fix: increase StreamScannerMaxBufferMB limit and add handling for gpt-5.4-nano prefix

setting/ratio_setting/model_ratio.go

@@ -510,6 +510,9 @@ func getHardcodedCompletionModelRatio(name string) (float64, bool) {
 		// gpt-5 匹配
 		if strings.HasPrefix(name, "gpt-5") {
 			if strings.HasPrefix(name, "gpt-5.4") {
+				if strings.HasPrefix(name, "gpt-5.4-nano") {
+					return 6.25, true
+				}
 				return 6, true
 			}
 			return 8, true