fix(dev): tenant-registry default port :8080 → :8090

Keycloak owns :8080 in the dev stack (docker-compose binds host:8080).
Running tenant-registry on the same port made 'make dev' refuse to
boot. Bump the default to :8090 across config, Makefile, Dockerfile,
.env.example, and README. ADDR env var still overrides if needed.

Production is unaffected — each service is in its own Orca container
with its own port-namespace.

Refs: M5.1 (unblocks portal local dev)

Dockerfile

@@ -11,5 +11,5 @@ FROM gcr.io/distroless/static-debian12:nonroot
 WORKDIR /
 COPY --from=build /out/tenant-registry /tenant-registry
 USER nonroot:nonroot
-EXPOSE 8080
+EXPOSE 8090
 ENTRYPOINT ["/tenant-registry"]