Migrate button component to components/button

[google-labs-jules]

Migrates the button component to components/button while maintaining backward compatibility.

• Moves button/ contents to components/button/.
• Updates internal imports to point to the correct locations.
• Creates re-exports in button/ for public APIs and Sass files.
• Adds copyright headers to re-export files.

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PR created automatically by Jules for task 7481579433609604152 started by @asyncliz

[google-labs-jules]

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