Adds a Pixel Art Editor Component

[kkoppenhaver]

Summary

• Adds a new pixel-art-editor component: a 32×32 canvas editor with pencil, eraser, flood-fill, palette, and PNG export.
• Drawing state is pushed back to Retool as a base64 PNG data URL on every stroke/fill/clear, plus currentTool, currentColor, and isEmpty outputs and change / export events.
• Wrapped with @tryretool/custom-component-support; built with React 18 + TypeScript, zero external dependencies beyond the SDK.

Test plan

• npx retool-ccl dev boots the component against a Retool instance
• Pencil, eraser, and fill all mutate the canvas and update imageDataUrl
• Export PNG button downloads a 512×512 PNG and fires the export event
• disabled inspector toggle greys out the toolbar and blocks canvas input
• Gallery form at https://customcomponents.retool.com/ submitted with this PR URL

🤖 Generated with Claude Code

[github-actions]

Hey! Just a reminder, your PR has been open for a week but your component hasn't been approved yet.

That's because it also needs to be submitted on the gallery website:
https://customcomponents.retool.com/

This is the last step! It only takes a few minutes — once submitted, our team will review it and get it live in the gallery. 🚀