lz: track Sentrix EID assignment from LayerZero Labs

[satyakwok]

README notes the deploy uses placeholder EID 40998 until LayerZero Labs assigns the official Sentrix Testnet (and later mainnet) EID.

Status

• Sentrix Testnet deployment ready with EID=40998 (placeholder)
• Awaiting LayerZero Labs chain-integration form submission + queue position

Why track this

Once LZ Labs assigns the real EID, every deployed contract that references EID 40998 (DeployLZ-SentrixTestnet.s.sol constants, OApp configs, future Treasury deploys) needs to be re-deployed with the actual value. Tracking the swap-over here prevents a stale-EID rollout.

Acceptance

• Real testnet EID landed in scripts + docs
• Real mainnet EID landed (post-mainnet-deploy)
• Old placeholder-EID contracts retired or noted as abandoned

[satyakwok]

Application draft is in docs/lz-labs-application.md (referenced from the expanded README in #6). Submission via forms.layerzero.foundation or LZ Discord #chain-integration is operator-side.