feat/outcome-token-contract

[luhrhenzthedev]

Summary

• Add contracts/outcome-token/ crate to the workspace — mint/burn YES/NO tokens scoped to (market_id, user)
• Auth-gate: only the registered market_contract can call mint and burn, enforced via require_auth() at the Soroban layer
• Admin can rotate the market contract address via set_market_contract

Changes

• contracts/outcome-token/ — new crate with error, types, storage, events, lib, and test modules
• Cargo.toml — added contracts/outcome-token to workspace default-members
• README.md — added contract status table and build step for the new crate

Test plan

• initialize stores config and rejects double-init
• mint increases per-user balance and total supply; rejects zero amount
• YES and NO balances are independent; balances are isolated across markets
• burn decreases balance and supply; rejects insufficient balance and zero amount
• set_market_contract succeeds for admin, returns Unauthorized for non-admin

closes #265

[Mimah97]

LFG