add gpt-5.4-mini, gpt-5.4-nano to copilot response models

Author: joshbarrington

pkg/model/provider/provider.go

@@ -553,6 +553,8 @@ func isCopilotResponsesModel(model string) bool {
 	codex := map[string]bool{
 		"gpt-5.3-codex": true,
 		"gpt-5.2-codex": true,
+		"gpt-5.4-mini":  true,
+		"gpt-5.4-nano":  true,
 	}
 	return codex[model]
 }