Switch from tsup to unbuild

[IanMitchell]

Since we use unbuild for discord-verify, and tsup does not work, we should convert create-ikit-app to run unbuild as well to simplify dependencies and toolchains.

[IanMitchell]

Pinning this as a good first issue for potential contributors. To accomplish this, we should remove the tsup dependency and update the create-ikit-app package scripts to use unbuild instead. If necessary, we can use a config similar to the one in discord-verify