Add LayerZero round-trip test — full bridge proven end-to-end

Shipped, not slipped.

Add LayerZero round-trip test — full bridge proven end-to-end — and the bridge got a little sharper for it.

test/RoundTrip.t.sol via TestHelperOz5 (2 local endpoints): - bridge IN : BSC vault locks CTB -> Base OFT mints (minus 0.30% fee) - fee skimmed to FeeTreasury; vault reserve == minted supply (1:1 invariant) - bridge OUT : Base OFT burns -> BSC vault unlocks; total supply conserved Deps for the harness: GNSPS/solidity-bytes-utils + LayerZero v1 (ULN mocks); remappings + README updated. forge test => 6 passed, 0 failed.

Under the hood it's the same promise: lock on BSC, mint 1:1 on Base, hold your own keys. See you on the other side.