Dev (latest main)

Add dev deploy pipeline alongside prod release flow

Every push to main now builds and deploys to dev.scriptyard.minimalhumans.com
via an upserted 'dev' prerelease, while pushing a vX.Y.Z tag still cuts the
real prod release as before. Both environments share one deploy script,
selected via ?env=dev, so the dev release tag never collides with prod's
/releases/latest lookup.