Implement dispute resolution voting

[justwe-bot]

Fixes #14

Summary

• Add member-based dispute voting through vote_on_dispute(member, group_id, approve).
• Track approve/reject vote counts and prevent duplicate votes per dispute.
• Add configurable dispute quorum with a 50% default and auto-resolve disputes when approving votes exceed quorum.
• Keep the existing admin/protocol-admin dispute resolution path intact.

Verification

• cargo test
• cargo build

Note: cargo build --target wasm32-unknown-unknown --release could not be completed locally because the Rust wasm32-unknown-unknown target is not installed and rustup target add wasm32-unknown-unknown stalled while downloading the component.

Bounty note: requesting assignment/consideration if #14 is still bounty-eligible.

[justwe-bot]

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