feat(auth): centralize token store management and enhance persistence

- Introduced `RegisterTokenStore` and `GetTokenStore` to centralize token store access.
- Replaced direct file operations with a unified token persistence API.
- Updated all components to use the shared token store for consistent behavior.
- Improved logging for token save operations to include file paths.

cmd/server/main.go

@@ -17,6 +17,7 @@ import (
 	"github.com/router-for-me/CLIProxyAPI/v6/internal/config"
 	_ "github.com/router-for-me/CLIProxyAPI/v6/internal/translator"
 	"github.com/router-for-me/CLIProxyAPI/v6/internal/util"
+	sdkAuth "github.com/router-for-me/CLIProxyAPI/v6/sdk/auth"
 	log "github.com/sirupsen/logrus"
 	"gopkg.in/natefinch/lumberjack.v2"
 )
@@ -185,6 +186,9 @@ func main() {
 		NoBrowser: noBrowser,
 	}
 
+	// Register the shared token store once so all components use the same persistence backend.
+	sdkAuth.RegisterTokenStore(sdkAuth.NewFileTokenStore())
+
 	// Handle different command modes based on the provided flags.
 
 	if login {