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)

.env.example

@@ -0,0 +1,11 @@
+# tenant-registry — local dev environment.
+#
+# Copy to .env.local (gitignored) and edit. The service reads env vars
+# directly via internal/config; this file is just documentation.
+
+APP_ENV=dev
+ADDR=:8090
+KEYCLOAK_ISSUER=http://localhost:8080/realms/breakpilot-dev
+
+# Postgres DSN — unused by the skeleton (in-memory store). Wired up in M4.1.
+# DATABASE_URL=postgres://platform:platform-dev-pass@localhost:5432/platform?sslmode=disable