Add storage-tier documentation for batch_claim

[greatest0fallt1me]

Description

This is a smart-contract issue for the GrantFox FWC26 campaign (Stellar Wave). Document batch_claim's storage keys with tier (Instance/Persistent/Temporary) and rationale.

Requirements and Context

• Implement per the description above
• Add focused tests for the change
• Document any API/visible changes
• Adhere to repo's lint and code style
• Must be secure, tested, and documented

Suggested Execution

1. Fork the repo and create a branch
2. Implement changes:
   • contracts/batch_claim/docs/storage.md
3. Test and commit; open a PR with Closes #704 in the body

Guidelines

• Minimum 95% test coverage with cargo test
• require_auth on every state-changing entrypoint
• Overflow-safe math; no unwrap() in production paths
• Clear NatSpec-style /// rustdoc
• Timeframe: 96 hours

[Bug00Joe]

@Bug00Joe has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hi Maintainer, I would like to work on this issue, thank you.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Bug00Joe to this issue.

[drips-wave]

Congratulations, @Bug00Joe! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

🧑‍💻 @Bug00Joe: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[greatest0fallt1me]

Hey @Bug00Joe 👋 — you've been assigned to this issue based on your DripsWave application.

Quick reminders:

• Draft PR early and link it with Closes #<issue-number> so the DripsWave bot auto-closes.
• Please respect the 4 assignments per org cap (DripsWave auto-unassigns beyond that).
• Ping in Discord for questions or unblocks: https://discord.gg/WC53JxDqx

Looking forward to your PR — good luck! 🚀

[Bug00Joe]

Before picking this up: I can't find a batch_claim contract anywhere in main — no contracts/batch_claim/ directory, and a full-repo search (GitHub code search + local grep on a fresh clone) turns up zero references to batch_claim in source or docs. The existing contracts are: admin, checkpoint, cold, freeze, helpers, hot, limits, migrate, registry, revenue_pool, settlement, upgrade, validators, vault, whitelist, yield.

For reference, #732 ("Add contract-error enum expansion for batch_claim") has the same issue — it was closed as completed via #766, but that PR only touched contracts/settlement, not batch_claim.

Could a maintainer confirm whether batch_claim lives on a different branch/fork that should be the PR base, or whether this issue (and #732) were generated against a contract that hasn't been merged yet? Happy to pick this up once there's a real target to document.