Implement zero-amount and dust transaction handling

[Smartdevs17]

Description

Zero-amount and dust transactions can cause edge cases in accounting. Implement proper handling with clear semantics.

Acceptance Criteria

• Zero-amount deposit/borrow/repay rejection
• Dust accumulation prevention (minimum transaction size)
• Dust sweep mechanism for users
• Rounding direction consistency (depositor-friendly)
• Gas-efficient dust checking
• Comprehensive edge case tests

Technical Scope

• stellar-lend/contracts/hello-world/src/test_zero_amount.rs
• stellar-lend/contracts/lending/src/
• docs/ZERO_AMOUNT_SEMANTICS.md
• Edge: precision loss in interest calculation, dust from liquidations, rounding asymmetry

[TUPM96]

Opened PR #399 to implement the zero-amount and dust transaction handling: #399

Verification completed:

• cargo fmt -p stellarlend-lending -- --check
• cargo check -p stellarlend-lending
• cargo test -p stellarlend-lending -- --test-threads=4
• git diff --check

[Properprogress1]

@Properprogress1 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Can I work on this please

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Properprogress1 to this issue.

[drips-wave]

Congratulations, @Properprogress1! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @Properprogress1: 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

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