neovide: install desktop file and icons under Linux

[zeitue]

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• I did not use AI/LLM to create this PR, or I disclosed the tool/model below and reviewed its output; I did not attribute commits to AI and will answer maintainer questions and review comments myself without AI/LLM.

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The brew Neovide formula does not install the desktop file or icons on LInux. This is needed for immutable distros like Blufin, Bazzite, Aurora, and defenestraOS to show the launcher for Neovide.

So this PR just adds these files to the brew installation from the pulled archive.

I've read through the Contribution process, I did not check the first box because I am not sure if I got everything.

AI was used to verify code and PR process (Gemini, Claude).

[github-actions]

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[SMillerDev]

Can't cargo install these in the right locations? This seems very fragile