fix: add proof-of-skill on-chain verification oracle

[rotimitimilehinsamuel-ops]

Overview

This PR adds a Soroban-based Proof-of-Skill On-Chain Verification Oracle that verifies official FIDE and national chess titles (GM, IM, FM, CM) through trusted oracle nodes, records attested credentials bound to Stellar public keys, and mints non-transferable Soulbound Title Badges — with multi-oracle threshold signature verification (2-of-3) and a revocation path for fair-play violations or FIDE sanctions.

Related Issue

Changes

🏆 On-Chain Title Verification Oracle

• [ADD] contracts/title_badge/src/lib.rs

  • Soroban contract exposing submit_proof, verify_title, mint_badge, revoke_badge, and get_title_record.
  • Requires 2-of-3 trusted verifier Ed25519 signatures before any FIDE title (GM/IM/FM/CM) is accepted on-chain.
  • Soulbound badge logic — no transfer or sell entry points; badge permanently bound to the owner's Stellar public key.

• [ADD] contracts/title_badge/src/storage.rs + contracts/title_badge/src/error.rs

  • Persistent storage for verifier keys, threshold configuration, verified title metadata, badge ownership, and revocation flags.
  • Typed error codes for unauthorized verifier, insufficient threshold signatures, duplicate proof, revoked title, and already-minted badge.

• [ADD/MODIFY] contracts/Cargo.toml + contracts/title_badge/Cargo.toml

  • Adds soroban-sdk dependencies and package metadata for building, testing, and deploying the title badge contract.

• [MODIFY] .github/workflows/soroban-deploy.yml

  • CI/CD workflow that runs cargo test -p title_badge, enforces cargo clippy -- -D warnings, and deploys the verified contract to Stellar testnet.

Verification Results

cargo test -p title_badge
✅ 15/15 passed

cargo clippy -p title_badge -- -D warnings
✅ No warnings

Live acceptance check:
✅ 2-of-3 oracle threshold signature verification passing
✅ Soulbound badge minted; transfer/sale entry points absent
✅ Revocation function clears badge and flags title record
✅ Contract deployed to Stellar testnet

Acceptance Criteria	Status
Multi-oracle threshold signature verification (2 of 3 trusted verifiers)	✅ 2-of-3 Ed25519 threshold enforced before title mint
Soulbound token logic preventing transfer or sale of title badges	✅ No transfer/sale entry points; badge permanently bound to owner
Revocation function in case of fair-play violations or FIDE sanctions	✅ revoke_badge clears badge and sets revoked status
FIDE title credentials recorded and attested on-chain	✅ GM/IM/FM/CM titles stored with FIDE ID proof and oracle attestations

Closes #1151

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