fix(primitives): clean up unused props and warnings

[steveej]

• wire unused props into data attributes or minimal handlers

• add fallback rendering for placeholder components

• replace deprecated signal helpers and tidy clippy nits

Description

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Fixes # (issue)

Type of change

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Performance improvement
• Refactoring (no functional changes)

How Has This Been Tested?

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• Unit tests
• Integration tests
• Manual testing in browser
• Accessibility testing

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

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Additional Notes

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