HSK's published mainnet genesis sets isthmusTime but omits pragueTime; op-geth's
OP-Stack validation rejects it ('PragueTime (<nil>) must equal IsthmusTime'), so
geth init aborts and the EL runs on a stale chainconfig. testnet genesis correctly
sets pragueTime=isthmusTime. Adding it here makes init pass. (Runtime fork activation
is handled by GETH_OVERRIDE_* in vibe-node geth.env; this fixes init + matches testnet.)
Co-Authored-By: Claude <noreply@anthropic.com>