[CO-04] Validate restaurant_id against RestaurantRegistry in place_order()

[Leothosine]

Problem

contracts/order/src/lib.rs:125-135 - place_order() accepts any restaurant_id: u64 without cross-contract validation:

pub fn place_order(env: Env, customer: Address, restaurant_id: u64, items: Vec<OrderItem>, ...) -> u64 {
    customer.require_auth();
    // No call to RestaurantRegistry to verify restaurant_id exists or is active
}

Orders can be placed against ghost restaurant IDs. The payment escrow will fund a wallet address that may not exist, permanently locking customer funds.

Proposed Solution

1. Add restaurant_registry_address: Address to the Order contract's initialize() and store in persistent storage
2. In place_order(), make a cross-contract call:

let registry_client = RestaurantRegistryClient::new(&env, &registry_addr);
let restaurant = registry_client.get_restaurant(&restaurant_id);
if !restaurant.is_active { panic!("restaurant is not active"); }

Acceptance Criteria

• place_order() with a non-existent restaurant_id panics with "restaurant not found"
• place_order() for an inactive restaurant panics with "restaurant is not active"
• Happy-path test with a valid active restaurant passes
• Cross-contract call is mocked via MockRestaurantRegistry in unit tests
• initialize() stores the registry address and all existing tests are updated

[Menjay7]

Hi! I came across this issue and would love to work on it. I have experience with similar tasks and I'm confident I can investigate, implement a clean solution, and thoroughly test it before submitting a PR. If the issue is still open, I would appreciate it if you could assign it to me. Thank you!

[AbdulmujibOladayo]

Hey maintainer. I have a proven track record and already understand the codebase and how to implement this issue without obstacles.

[grantfox-oss]

🦊 GrantFox — @AbdulmujibOladayo has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #282)
2. Your PR will be reviewed by the tosirano maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

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

@AbdulmujibOladayo's PR #293 was approved and merged by @Leothosine.

🏆 @AbdulmujibOladayo: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (258 total points). Track your full progress on GrantFox.

👏 Great work, @AbdulmujibOladayo! Keep contributing to tosirano.