feat: audit-clickhouse module with ClickHouse analytics

- Three endpoints: /funnel, /funnel/gates, /hypotheses
- SQL files extracted to resources/sql/
- 10 tests: FunnelResult, HypothesisResult, AuditController
- Validation: days <= 0 → 400 Bad Request
- First production data: AR=53.4%, H6=21K chain declined