feat: merge optional presets back into core

[Hugos68]

Linked Issue

Closes #3712

Description

Merges the optional stylesheet into core.

Checklist

Please read and apply all contribution requirements.

• Your branch should be prefixed with: docs/, feature/, chore/, bugfix/
• Contributions should target the main branch
• Documentation should be updated to describe all relevant changes
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• Run pnpm test in the root of the monorepo
• If you modify /package projects, please supply a Changeset

Changesets

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1. Navigate to the root of the monorepo in your terminal
2. Run pnpm changeset and follow the prompts
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[changeset-bot]

🦋 Changeset detected

Latest commit: 940ffa2

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@skeletonlabs/skeleton	Minor

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Project	Deployment	Preview	Comments	Updated (UTC)
themes.skeleton.dev	Building	Preview	Comment	Sep 11, 2025 4:43pm
www.skeleton.dev	Ready	Preview	Comment	Sep 11, 2025 4:43pm

[Hugos68]

@endigo9740 Awaiting a review from you

[endigo9740]

@Hugos68 you have my go ahead to merge after these small text changes are implemented.

Thanks for being thorough and updating the docs and extra monorepo imports. Onboarding looks to be so much simpler!