Fix argument validation for --set-default flag

- Replace static cobra.RangeArgs(1, 2) with custom validation function
- Allow 0 arguments when --set-default flag is provided
- Maintain 1-2 argument requirement for normal workspace operations
- Resolves issue where 'brev open --set-default cursor' failed with arg validation error

Co-Authored-By: Alec Fong <alecsanf@usc.edu>

Author: devin-ai-integration[bot]

pkg/cmd/open/open.go

@@ -65,7 +65,13 @@ func NewCmdOpen(t *terminal.Terminal, store OpenStore, noLoginStartStore OpenSto
 		Short:                 "[beta] open VSCode or Cursor to your workspace",
 		Long:                  openLong,
 		Example:               openExample,
-		Args:                  cmderrors.TransformToValidationError(cobra.RangeArgs(1, 2)),
+		Args: cmderrors.TransformToValidationError(func(cmd *cobra.Command, args []string) error {
+			setDefaultFlag, _ := cmd.Flags().GetString("set-default")
+			if setDefaultFlag != "" {
+				return cobra.NoArgs(cmd, args)
+			}
+			return cobra.RangeArgs(1, 2)(cmd, args)
+		}),
 		ValidArgsFunction:     completions.GetAllWorkspaceNameCompletionHandler(noLoginStartStore, t),
 		RunE: func(cmd *cobra.Command, args []string) error {
 			if setDefault != "" {