Extract build_railpack_static_image() into its own method, prevent port
override when is_static is set, bump Railpack to 0.22.0, and improve
test setup with beforeEach and correct polymorphic env var fields.
Move buildpack switching cleanup from Livewire component to Application model's boot lifecycle. This improves separation of concerns and ensures cleanup happens consistently regardless of how the buildpack change is triggered. Also clears Dockerfile-specific data when switching away from dockerfile buildpack.
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Co-Authored-By: Claude <noreply@anthropic.com>