🎨 Palette: Add Focus Trap hook for accessible modals

[google-labs-jules]

This PR introduces a useFocusTrap hook to improve accessibility in modals, specifically applied to the TutorialModal component.

💡 What:

• Created src/hooks/useFocusTrap.ts which manages focus trapping (keeping focus inside the modal), handles the Escape key, and restores focus to the trigger element when closed.
• Updated src/components/education/TutorialModal.tsx to utilize this hook.
• Added src/__tests__/useFocusTrap.test.tsx to verify the behavior.

🎯 Why:

• Previous implementation of TutorialModal allowed keyboard users to tab out of the modal, getting lost in the background content.
• It also lacked standard "Escape to close" behavior in some contexts (though StoryModal had it locally).
• Focus restoration is a WCAG requirement so users know where they are after closing a dialog.

♿ Accessibility:

• Focus Trap: Prevents focus from leaking to the background.
• Escape Key: Allows easy closure of the modal.
• Focus Restoration: Returns focus to the element that opened the modal.
• Initial Focus: Ensures screen readers start reading the modal content correctly.

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PR created automatically by Jules for task 10959579840997538626 started by @albertoivo

[google-labs-jules]

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