🎨 Palette: Add accessible clear button to Command Palette search input

[TheDragonSoft]

💡 What:

1. Added onClear and clearLabel="Clear command search" to the <Input> search component in CommandPalette.tsx.
2. Added onMouseDown={(e) => e.preventDefault()} to the clear button inside Input.tsx to prevent clicking clear from blurring the text input element, ensuring keyboard focus stays inside the search box.

🎯 Why:
Allows users to quickly clear their search term in the Command Palette and continue typing immediately without having to re-focus the input box.

♿ Accessibility:
Includes explicit ARIA label clearLabel for screen readers and maintains keyboard focus within the search field on mouse interaction.

---

PR created automatically by Jules for task 8985668180005026818 started by @TheDragonSoft

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.