fix(auth): scope native keyring backends to desktop targets

Author: zssz

.changeset/fix-auth-keyring-backend.md

@@ -2,4 +2,4 @@
 "@googleworkspace/cli": patch
 ---
 
-Fix `gws auth login` encrypted credential persistence by enabling native keyring backends for the `keyring` crate instead of silently falling back to the in-memory mock store.
+Fix `gws auth login` encrypted credential persistence by enabling native keyring backends for the `keyring` crate on supported desktop platforms instead of silently falling back to the in-memory mock store.