Separate write/read DataSources, a JPA command side, and two interchangeable
projection listeners (sync and @Async) demonstrating the real latency-versus-
freshness trade-off CQRS forces. Includes a reflection-based proof that the
query side has no dependency on the write side, and a real failure/fix
transcript for the -parameters compiler flag this standalone reactor doesn't
inherit from spring-boot-starter-parent.
