refactor: extract DefaultAuthDir constant per review feedback

internal/config/config.go

@@ -22,6 +22,7 @@ import (
 const (
 	DefaultPanelGitHubRepository = "https://github.com/router-for-me/Cli-Proxy-API-Management-Center"
 	DefaultPprofAddr             = "127.0.0.1:8316"
+	DefaultAuthDir               = "~/.cli-proxy-api"
 )
 
 // Config represents the application's configuration, loaded from a YAML file.

internal/util/util.go

@@ -73,9 +73,10 @@ func SetLogLevel(cfg *config.Config) {
 
 // ResolveAuthDir normalizes the auth directory path for consistent reuse throughout the app.
 // It expands a leading tilde (~) to the user's home directory and returns a cleaned path.
+// If authDir is empty, it defaults to ~/.cli-proxy-api.
 func ResolveAuthDir(authDir string) (string, error) {
 	if authDir == "" {
-		authDir = "~/.cli-proxy-api"
+		authDir = config.DefaultAuthDir
 	}
 	if strings.HasPrefix(authDir, "~") {
 		home, err := os.UserHomeDir()