fix: wire config_freeze.rs into set_config() authorization path

[Icahbod]

Overview

config_freeze.rs implements freeze/unfreeze but these functions are never called from set_config(). The freeze flag has zero gating effect.

Evidence

File: apexchainx_calculator/src/config_freeze.rs — implements freeze logic
File: apexchainx_calculator/src/lib.rs — set_config() has no freeze check

Impact

• Admin who calls freeze_config() has false sense of security
• Config can still be changed despite freeze flag being set

Proposed Solution

Add require_not_frozen() check in set_config(). Expose freeze/unfreeze as admin-gated methods. Emit events.

Acceptance Criteria

• set_config() returns error when config is frozen
• Error uses clear variant (e.g., ConfigFrozen = 16)
• Admin can freeze/unfreeze via contract methods
• Freeze/unfreeze emit versioned events
• is_config_frozen() returns correct state
• Unfrozen state allows normal updates
• All existing tests pass

File Map

• apexchainx_calculator/src/config_freeze.rs
• apexchainx_calculator/src/lib.rs
• apexchainx_calculator/src/tests.rs

Testing Strategy

Unit: Freeze → attempt set_config → verify rejection. Unfreeze → verify success.

Labels: bug, high, security

Priority: High

Difficulty: Intermediate

Estimated Effort: 3h

[aliyuHabibu]

Hi, I'm a software engineer, I've gone through the issue and I can resolve it. Assign it to me thank you

[grantfox-oss]

🦊 GrantFox — @aliyuHabibu 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 #3)
2. Your PR will be reviewed by the ApexChainx 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!

@aliyuHabibu's PR #63 was approved and merged by @Icahbod.

🏆 @aliyuHabibu: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (401 total points). Track your full progress on GrantFox.

👏 Great work, @aliyuHabibu! Keep contributing to ApexChainx.