Refactor customization toolbar and sidebar button styles (#314994)

* Refactor sidebar action button styles and update AI customization toolbar layout

Co-authored-by: Copilot <copilot@github.com>

* Update hover color for customization link button to match session list items

Co-authored-by: Copilot <copilot@github.com>

* Reduce gap size in sidebar action button styles from 10px to 6px

* Refactor toolbar styles: remove unnecessary margins and adjust padding for alignment

* Refactor customization toolbar styles: remove margin-left from chevron and update padding comments for alignment

* Refactor button container styles for alignment and hover background consistency

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Co-authored-by: mrleemurray <mrleemurray@users.noreply.github.com>
Co-authored-by: Copilot <copilot@github.com>