Feature: Replace cross-env with pnpm shellEmulator

[Greenheart]

This change simplifies the development environment (and reduces dependencies to install for CI testing), since we already use pnpm which has this feature built-in.

I also documented the test case in Toast.test.tsx that fails when run with pnpm test-strict. It might be worth looking into if the test case could be written in a different way, but this is out of scope for this change so I opted for a comment instead.

[changeset-bot]

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Latest commit: 7574123

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