Ensure ImageEditor brush colour is updated when changed

[hannahblair]

Description

The brush colour wasn't changing when a different color was selected, so it was always being set to red. The issue was in the Brush.sveltes initialisation of selected_color. It was using a reactive statement that kept resetting the colour back to the default value every time any dependencies changed.

Closes: #9105
Closes: #9066

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[gradio-pr-bot]

🪼 branch checks and previews

•	Name	Status	URL
	Spaces	ready!	Spaces preview
	Storybook	ready!	Storybook preview
🦄	Changes	detected!	Details

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Install Gradio from this PR

pip install https://gradio-pypi-previews.s3.amazonaws.com/3856c9fe8930bf4aa63a1c513e68236bffd910fd/gradio-5.6.0-py3-none-any.whl

Install Gradio Python Client from this PR

pip install "gradio-client @ git+https://github.com/gradio-app/gradio@3856c9fe8930bf4aa63a1c513e68236bffd910fd#subdirectory=client/python"

Install Gradio JS Client from this PR

npm install https://gradio-npm-previews.s3.amazonaws.com/3856c9fe8930bf4aa63a1c513e68236bffd910fd/gradio-client-1.8.0.tgz

Use Lite from this PR

<script type="module" src="https://gradio-lite-previews.s3.amazonaws.com/3856c9fe8930bf4aa63a1c513e68236bffd910fd/dist/lite.js""></script>

[gradio-pr-bot]

🦄 change detected

This Pull Request includes changes to the following packages.

Package	Version
@gradio/imageeditor	patch
gradio	patch

• Maintainers can select this checkbox to manually select packages to update.

With the following changelog entry.

Ensure ImageEditor brush colour is updated when changed

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• If the bot has failed to detect any changes, or if this pull request needs to update multiple packages to different versions or requires a more comprehensive changelog entry, maintainers can update the changelog file directly.

[freddyaboulton]

Will take a look first thing tomorrow!

[freddyaboulton]

Sorry mis-clicked lol

[freddyaboulton]

Tested and works great @hannahblair !