Add the src/lib/economy service (GM baselines, deterministic per-period demand drift, price modifier computation, event emission) and the economy-tick bin. Gated by GameRules economy.enabled; period-idempotent with a cold-start observation gate.
Ultraworked with [Sisyphus](https://github.com/code-yeongju/oh-my-openagent)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
