Feat/cancel market

[aji70]

Implement cancel_market() for creator/admin

Summary

Implements the cancel_market() function so creators or admins can cancel markets before resolution and refund all committed USDC to participants. Closes #64

Changes

contracts/contracts/boxmeout/src/market.rs

• State & storage

  • Added STATE_CANCELLED = 3
  • Added PARTICIPANTS_KEY and ADMIN_KEY
  • Added MarketError::Unauthorized

• Initialization

  • Added admin: Address to initialize() (breaking change)

• Participants tracking

  • Append user to participants list in commit_prediction() for refunds on cancel

• cancel_market()

  • Requires caller to be creator or admin
  • Rejects cancel when market is RESOLVED or already CANCELLED
  • Refunds USDC to all participants (both commitments and revealed predictions)
  • Sets market state to CANCELLED
  • Emits MarketCancelled event

contracts/contracts/boxmeout/src/factory.rs

• Added get_admin() for future use

contracts/BUILD.md

• Updated initialize() example to include admin_address

Acceptance criteria

• Only creator or admin can cancel
• Refund all committed USDC to participants
• Transition status to CANCELLED
• Emit MarketCancelled event
• Block cancel on resolved markets
• Unit tests

Tests added

• test_cancel_market_creator_refunds_participants – creator cancels and refunds
• test_cancel_market_admin_refunds_participants – admin can cancel
• test_cancel_market_unauthorized – non-creator/non-admin fails
• test_cancel_market_resolved_fails – cannot cancel resolved market
• test_cancel_market_refunds_predictions – refunds revealed predictions

Breaking change

initialize() now takes admin as the 4th parameter:

// Before
initialize(market_id, creator, factory, usdc_token, oracle, closing_time, resolution_time)

// After
initialize(market_id, creator, factory, admin, usdc_token, oracle, closing_time, resolution_time)

[GoSTEAN]

@aji70 resolve conflict