[CT-11] Implement Multi-Booking Limit Validator per member tier in Rust

[devwums]

Problem

No on-chain enforcement prevents a member from holding more simultaneous active bookings than their tier permits. Members can bypass backend limits.

Proposed Solution

Create contracts/cntr/multi_booking.rs implementing pub fn get_booking_limit(tier: &str) -> u32 (Bronze: 2, Silver: 5, Gold: 10, Platinum: u32::MAX) and pub fn can_make_booking(tier: &str, current_active_bookings: u32) -> bool. Unknown tier strings default to Bronze limit. All implementation must live inside contracts/cntr/.

Acceptance Criteria

• File at contracts/cntr/multi_booking.rs
• Returns correct limits for all 4 known tier strings
• Unknown tier strings return the Bronze limit (2)
• can_make_booking returns false when current_active_bookings >= limit
• can_make_booking returns true when current_active_bookings < limit
• At least 6 unit tests
• Compiles with cargo test

[authenticeasy-sys]

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

can i take this

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

[drips-wave]

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

🧑‍💻 @authenticeasy-sys: 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 🌊