Migrate to Plasmo for easier cross-browser support

[cmgriffing]

Plasmo has more supported browser targets than the current boilerplate. With Plasmo we can add support for Edge and Brave.

[uncenter]

I'd recommend https://wxt.dev/ over Plasmo; growing quickly, very intuitive, active maintainer on GitHub and on Discord. Been using it for two extensions now, loving it! Has a guide/example workflow even on using one of their built-in wxt commands to publish to all stores of your choice (https://github.com/catppuccin/github-file-explorer-icons/blob/68eb57bc534674d698700aec6d27587e48b82c3d/.github/workflows/release-please.yml#L55-L70).