feat: add ferret icons

[itsfuad]

Description

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[itsfuad]

@PKief As per our previous discussion , I reduced the icon colors and used the material color standards.

Kindly review and provide your feedback on this.

[itsfuad]

@PKief Hi! Just following up on this PR. It adds ferret icon support to the material icon theme to cover projects using ferret‑prefixed files. Let me know if there are any changes or previews you'd like. Happy to update quickly.
Thanks!

[lucas-labs]

Hi @itsfuad,
these icons doesn't follow the material design style. Please make sure you read our contribution guide.

As a summary:

• We don't use outlines
• We don't use pure black (#000000) or white (#ffffff) colors, remember we need to support the largest amount of vscode themes as possible, including dark, light and contrast themes.
• We set a margin of at least 1px (at 16x16 px) around the icon.
• The shapes in the icons are too complex, the icon will be rendered as a 16px*16px image in vscode, all details that are smaller than 1px at that resolution will not be visible.

[itsfuad]

@lucas-labs thanks for the review. I can change:

1. outlines
2. pure black / white colors
3. adjust the margin space in the final revision.

Here is the adjustments. Is that okay?

And I'll use simple lock Icon and a simple Box instead of the mascot for the other 2 icons.