expense-service

Split expense port. Schema expense.

Default port	8083
Java counterpart	expense-service
Source	splick-backend-rust/services/expense-service

Read the Java service pages for tables, events, and Kong prefixes. The Rust port is expected to honor that contract. Document a divergence here in the same change that introduces it, and do not let the two writers share a schema.

Configuration names follow the Java service where the port has reached parity, plus DATABASE_URL, REDIS_URL, and SERVER_PORT. Do not commit .env.