Add invoice bulk recipient management

[Kingsman-99]

Label: complexity: high
Points: 200

Description

Adding many recipients one by one via add_recipient() is inefficient for large team invoices. This issue adds add_recipients_batch() allowing the creator to append up to 50 recipients with amounts in a single transaction before any payment is received.

Technical Context

Involves lib.rs — new add_recipients_batch(env, invoice_id: u64, new_recipients: Vec<Address>, new_amounts: Vec<i128>). Requires creator auth. Assert invoice.funded == 0. Assert new_recipients.len() == new_amounts.len(). Assert new_recipients.len() <= 50. Extend both Vecs and save.

Acceptance Criteria

• Requires creator auth
• Panics with "payments already received" if invoice.funded > 0
• Panics with "batch too large" if more than 50 recipients provided
• All new recipients and amounts appended correctly
• Test adds 5 recipients in batch, pays full new total, verifies all receive funds
• All existing cargo tests pass
• cargo clippy passes with zero warnings

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[Venrable18]

@Venrable18 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Good day maintainer..

I’m a full-stack and test integration developer…. 

Please assign this task to me…

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Venrable18 to this issue.

[TheBigWealth89]

@TheBigWealth89 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi maintainer, I have gone through the task description and will like to work on this please. Thank you

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[ahmadadebayo78-boop]

@ahmadadebayo78-boop has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I would like to work on this issue

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[drips-wave]

Congratulations, @ahmadadebayo78-boop! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @ahmadadebayo78-boop: 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.

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