Add validation that DisputeVoting voter cannot also be original disputer

[greatest0fallt1me]

Description

DisputeVoting in disputes.rs accepts a vote from the address that opened the dispute, biasing tallies. Reject any vote_on_dispute call where voter == disputer.

Requirements and Context

• Add an early check in DisputeManager::vote_on_dispute returning Error::DisputerCannotVote
• Update disputes.rs and tests
• Emit DisputeVoteRejectedEvent (extend events.rs if needed)
• Must be secure, tested, and documented
• Should be efficient and easy to review

Suggested Execution

1. Fork the repo and create a branch

   git checkout -b fix/dispute-self-vote-rejection

2. Implement changes
   • contracts/predictify-hybrid/src/disputes.rs
   • contracts/predictify-hybrid/src/err.rs
3. Test and commit
   • cargo test -p predictify-hybrid dispute -- --nocapture
   • Cover edge cases: disputer != voter, disputer == voter
   • Include test output and notes in the PR

Example commit message

fix: reject self-vote by dispute opener in DisputeManager

Acceptance Criteria

• Self-vote test fails with DisputerCannotVote
• Existing legitimate vote path unchanged
• No unwrap() introduced
• Documented in disputes.rs rustdoc

Guidelines

• require_auth(&voter) must precede the new check
• Minimum 95% coverage
• Clear documentation and inline comments
• Timeframe: 96 hours

[Joseph-1-Duro]

@Joseph-1-Duro has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi team, i would love to work on your project.

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[drips-wave]

Congratulations, @Joseph-1-Duro! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

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[grantfox-oss]

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

@Joseph-1-Duro's PR #645 was approved and merged by @greatest0fallt1me.

🏆 @Joseph-1-Duro: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (331 total points). Track your full progress on GrantFox.

👏 Great work, @Joseph-1-Duro! Keep contributing to Predictify-org.