Epic: Account & Authentication

✅ Mission ACCOUNT-SYSTEM: Multi-Character Architecture

• JWT Login: Game clients can authenticate via JWT, enabling persistent sessions.
• Multi-Character Support: Backend supports multiple characters per account (limit 3).
• Secure Hashing: All new accounts use Argon2id password hashing.

✅ Mission FIX-LOGIC-CORE-TESTS: Test Suite Stability

• Test Suite Stability: logic-core test suite is now fully green.
• Bug Fixes: Fixed actual logic bugs in combat and DB schema alignment issues.

✅ Mission APIS-COVERAGE: Ensuring 100% Test Coverage

• Reliability: The entire API surface is now covered by automated tests.
• Security: The sql_safety admin tool has strict safeguards.