[Docs] Write a Soroban contract reference for lending_pool, loan_manager, multisig_governance, and remittance_nft

[grantfox-oss]

Telegram (ask questions / claim the issue here first): https://t.me/+DOylgFv1jyJlNzM0

Why this matters

wiki/contract-state-machine.md covers loan lifecycle at a high level, but there is no reference listing each contract's public functions, parameters, emitted events, error codes, and storage keys. This is essential for anyone integrating with or auditing the contracts.

Acceptance criteria

• For each of the four contracts, list public functions with signatures and a one-line description
• Document emitted events and their topics/data
• Document the error enums and what triggers each variant
• Document the storage keys and their storage class (instance/persistent/temporary) and TTL expectations

Files to touch

• contracts-reference.md (new)
• wiki/contract-state-machine.md

Out of scope

• Formal verification writeups
• Gas/size benchmarking docs

[Macnelson9]

Hi team, I'd like to take on this issue.

I specialize in Rust development, smart contract engineering, and frontend development with Next.js, React, and TypeScript. My experience allows me to bridge on-chain functionality with intuitive user experiences, ensuring both technical correctness and usability.

I'll follow the existing codebase conventions, communicate progress clearly, and deliver a high-quality solution within the expected timeline.

Thank you for your consideration.

[iyanumajekodunmi756]

Hi maintainer, I would love to work on this issue. I have studied the details of the issue description and I understood the requirements. I shall deliver with qualitative feedback and promptly.

[grantfox-oss]

🦊 GrantFox — @iyanumajekodunmi756 has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #3)
2. Your PR will be reviewed by the LabsCrypt maintainers

Good luck! Track your progress on GrantFox.