chore: address informative security considerations

[mialbu]

Summary

Addresses the informative audit findings (XGAS-03).

Adds security and integration guidance for:

• absence of emergency pause / kill-switch controls as an intentional immutable/no-admin design choice;
• possible forced GAS surplus where address(this).balance > totalSupply();
• standard ERC-20 approval race behavior and recommended approval patterns;
• Git submodule dependency and review expectations.

The update also clarifies the repository’s Git submodule model and dependency review workflow, including the role of superproject gitlink SHAs and reproducible submodule checkout behavior.

Notes

No production Solidity behavior was changed.