Discuss possibility to generate islands theme as a specific preset of generic one

We can move things like colors, fonts, etc into variables and then on, for example, postinstall stage generate current `islands` theme on FS. And as so we will still be able to split bundles but also provide users with ability to customise their own themes with some simple web interface.

No files, tests, or entry points are named. Start by locating the current islands theme and the postinstall and bundle-generation flow, then clarify how variables, preset generation, and user customization should work before defining what a complete implementation would require.

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