feat: implement Reversi with board flipping and positional scoring

[miguelnietoa]

Closes #76

Summary

• Implements a complete Reversi (Othello) game as a Soroban smart contract using Cougr's ECS pattern
• Components: BoardComponent, TurnComponent, GameStatusComponent, ScoreComponent stored as a single ECSWorldState
• Systems pipeline in submit_move: validation → flip resolution → scoring → turn/pass → end condition
• 14 unit tests covering init, move validation, horizontal/vertical/diagonal flips, score tracking, turn management, and re-init guard
• README with ECS design, contract API, rules, implementation patterns, and Testnet deployment instructions
• MATCH_LOG documenting a real Testnet game (Black wins 36–28 in 60 moves)

Test plan

• cargo test — 14/14 passing
• cargo clippy --all-targets --all-features -- -D warnings — clean
• cargo fmt --check — clean
• Deployed and played to completion on Testnet (CAQCSRHZZ4O3LN3LEQVF3JQ3H7UI7XPR65WWSCWKUWDKITSEFVRHF2OW)

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[salazarsebas]

LGTM

[salazarsebas]

Hey @miguelnietoa , please just fix the format error

[miguelnietoa]

Done, thanks @salazarsebas!