PseudoStates: Preserve URL globals on story change

[Sidnioulz]

Closes #32221

What I did

The decorator's parameter->globals sync effect was emitting UPDATE_GLOBALS
with an empty config on every story that didn't declare 'parameters.pseudo'.
On initial load, this overwrote pseudo state globals supplied via URL or
toolbar (e.g. ?globals=pseudo.focusVisible:!true) with {}, dropping the
user's selection before it could be applied.

Skip the sync when the parameter has no pseudo states to push, so URL and
toolbar globals survive on stories that don't set the parameter themselves.

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

• Navigate to SB instance
• Open a story without a pseudostates param, e.g. Components / Select / *
• Set a pseudo state
• Navigate to the next story
• Notice it persists
• Unset it
• Navigate to the next story
• Notice it stays unset

🦋 Canary release

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core team members can create a canary release here or locally with gh workflow run --repo storybookjs/storybook publish.yml --field pr=<PR_NUMBER>

Summary by CodeRabbit

Release Notes

• Bug Fixes

  • Fixed an issue where pseudo-state styling could be unintentionally cleared when navigating between stories that don't define pseudo-states, ensuring toolbar selections persist correctly.

• Tests

  • Added end-to-end regression test to verify pseudo-state decorators persist across unrelated story navigation.

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