Add missing sandbox icons and refactor ecosystem SVGs

[astrobot-houston]

Originally proposed by @corymsmith in #298. Their description is reproduced verbatim below.

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• Add icons for sandboxes without icons (boxd, exe.dev, islo, and mirage)
• Extracts svgs out to a new file to clean up the ecosystem page
• Removes smolvm for now since the link 404's as its not currently available (see Add smolvm sandbox connector #101)
• Uses the sandbox / ecosystem items with icons on the homepage.

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Original implementation from #298 by @corymsmith

[corymsmith]

Updates this section:

To look like this:

[corymsmith]

@FredKSchott I find the contribution flow quite confusing when its just docs updates. Totally get the issue with AI slop and wanting to prevent that.

PR is ready to merge, ran check and verified everything visually as well.

This all started because I noticed the current link for smolvm 404's as the page doesn't exist since the integration isn't ready.

[corymsmith]

I also have an icon for https://github.com/smol-machines/smolvm when its ready but I noticed there are 2 of them with the same name:

• The one referenced in a previous PR: https://github.com/smol-machines/smolvm
• And this one:
  • https://docs.celesto.ai/smolvm/introduction
  • https://github.com/CelestoAI/SmolVM