Add optional max supply cap per creator at registration to enable enforced key scarcity

[Chucks1093]

Summary

Every creator on the platform currently has unlimited key supply determined only by demand. Some creators may want to hard-cap the number of keys that can ever exist for them — creating genuine scarcity that cannot be undone. Adding an optional max_supply field at registration gives creators this control at the contract level, enforced on-chain with no way for anyone to override it after the fact.

Scope

• Add optional max_supply: Option<u32> parameter to register_creator
  • If None, supply is uncapped (current behavior, fully backwards-compatible)
  • If Some(n), the value is stored in creator state and n must be greater than zero
• At the start of buy, check if current_supply + amount_to_buy > max_supply and panic with a new SupplyCapExceeded error if true
• Add get_max_supply(creator_id) -> Option<u32> view function
• The cap is immutable after registration — no function may update it

Acceptance Criteria

• Registration with None behaves identically to current behavior
• Registration with Some(0) is rejected with an appropriate error
• Buy that would exceed the cap reverts with SupplyCapExceeded
• Buy that stays within the cap succeeds normally
• get_max_supply returns None for uncapped creators and the cap value for capped ones
• No function exists that can update the cap after registration
• Unit tests cover: uncapped buy, capped buy within limit, capped buy at limit, capped buy exceeding limit

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[Cyberking99]

Hello,

I am a smart contract and full-stack developer interested in contributing to this issue. I am experienced with hands-on experience in Rust, Soroban, Go, Cairo, Solidity, and TypeScript.

I am passionate about building secure and scalable blockchain solutions, with a strong focus on writing clean, maintainable code. Based on the scope of this issue, I am confident I can deliver a complete solution within 24 hours of assignment.

I would appreciate the opportunity to contribute and help move this forward.

[ZuLu0890]

I would love to work on this issue

[grantfox-oss]

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