Add receipt registry with getReceiptByTxHash lookup

[Kingsman-99]

Description

src/receipt.ts generates payment receipts but provides no way to retrieve a previously generated receipt by its transaction hash. Once a receipt is created, callers must store it themselves with no SDK lookup support. This issue adds a local receipt registry with hash-based lookup.

Acceptance Criteria

• registerReceipt(receipt: PaymentReceipt): void exported — stores receipt keyed by receipt.txHash
• getReceiptByTxHash(txHash: string): PaymentReceipt | null exported — returns stored receipt or null
• getAllReceipts(): PaymentReceipt[] exported — returns all registered receipts ordered by receipt.timestamp ascending
• clearReceipts(): void exported for test teardown
• Registry is module-level (singleton) — not tied to any class instance
• All exported from src/index.ts
• Unit tests: register and retrieve by hash, unknown hash returns null, getAllReceipts order, clearReceipts empties registry

Context

• Target files: src/receipt.ts, src/index.ts
• PaymentReceipt type already defined in src/types/receipts.ts — do not duplicate it

[bobo-24]

Hi! I’m a full-stack developer with a strong blockchain background, and I’m confident I can resolve this issue quickly and effectively. I’ll deliver a clean, reliable solution with immediate attention to detail, ensuring it’s completed as soon as possible. Please assign it to me—I’m ready to get started right away.

[bobo-24]

Hi! I’m a full-stack developer with a strong blockchain background, and I’m confident I can resolve this issue quickly and effectively. I’ll deliver a clean, reliable solution with immediate attention to detail, ensuring it’s completed as soon as possible. Please assign it to me—I’m ready to get started right away.

[wendyamoni-creator]

Hi, I would love to work on this issue

[grantfox-oss]

🦊 GrantFox — @wendyamoni-creator has been assigned to this issue as part of the Third Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #613)
2. Your PR will be reviewed by the Stellar-split maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Third Campaign campaign!

@wendyamoni-creator's PR #725 was approved and merged by @Kingsman-99.

🏆 @wendyamoni-creator: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (48 total points). Track your full progress on GrantFox.

👏 Great work, @wendyamoni-creator! Keep contributing to Stellar-split.