Document the storage key namespace layout

[arisu6804]

Summary

Document the storage key namespace layout.

Context

Tracking issue for the RemitFlow smart contract. Open to contributors.

Acceptance criteria

• Implement the change described above
• Add or update automated tests
• Update the relevant documentation

[grantfox-oss]

🦊 GrantFox — @mitchellecm7 has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #86)
2. Your PR will be reviewed by the RemitFlow maintainers

Good luck! Track your progress on GrantFox.

[arisu6804]

Assigned, @mitchellecm7! Documenting the storage key namespace layout helps everyone reason about the contract's state.

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