refactor: replace payneteasy-audit+scripts with audit-clickhouse ClickHouse module

- Remove payneteasy-audit (bash wrapper) and scripts/
- Add audit-clickhouse: Spring Boot 3.4, Java 21, clickhouse-jdbc
- Three endpoints: /funnel, /funnel/gates, /hypotheses
- First production data: AR=53.4%, H6=21K chain declined, H4=3DS timeout
- Update .gitignore, .env.example, Makefile, README