[CourseRegistry] Require explicit completion integration configuration

[Kaylahray]

Description

Final course completion currently tolerates missing integration addresses by skipping badge minting or reward payout. This issue makes completion behavior explicit so production deployments cannot silently miss side effects.

User Story

As the Learnault Protocol,
I want to fail or explicitly configure completion side effects,
so that course completion never silently skips reward or badge issuance in production.

Requirements and Context

• Files: contracts/course-registry/src/lib.rs, contracts/course-registry/src/test.rs
• Define whether final completion requires RewardPoolAddress, BadgeNftAddress, or both
• If the selected integration is mandatory, revert when final completion is attempted without the configured address
• If optional behavior must remain supported, add an explicit mode flag rather than silently skipping work

Suggested Implementation

// 1. Add explicit completion integration configuration or policy flag.
// 2. On final module completion, enforce the chosen policy before side effects run.
// 3. Only allow silent skipping if the policy explicitly enables it.

Acceptance Criteria

• Final completion behavior is deterministic and documented when integration addresses are missing.
• Production-mode tests fail if required completion integrations are unset.
• The contract no longer silently drops badge minting or payout side effects without policy support.

Submission Guidelines

• Branch: feat/explicit-completion-integrations
• Depends on: [CourseRegistry] Trigger payout on course completion, [CourseRegistry] Trigger badge minting on completion
• PR: feat(course-registry): require explicit completion integration configuration

[Martins-594]

Hi, I'd like to work on this issue. I've gone through the description and acceptance criteria and I'm confident I can deliver it. I'll make sure every acceptance criterion is met and submit a clean, tested PR. Please assign it to me.

[syed-ghufran-hassan]

I have added explicit completion policies (Optional/RewardRequired/BadgeRequired/BothRequired) to CourseRegistry, ensuring badge minting and reward payouts are never silently skipped in production; Optional policy maintains backward compatibility while required policies enforce integration configuration before course completion.