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)

internal/config/config_test.go

@@ -17,8 +17,8 @@ func TestLoad_defaults(t *testing.T) {
 	if cfg.Env != "dev" {
 		t.Errorf("Env = %q, want dev", cfg.Env)
 	}
-	if cfg.Addr != ":8080" {
-		t.Errorf("Addr = %q, want :8080", cfg.Addr)
+	if cfg.Addr != ":8090" {
+		t.Errorf("Addr = %q, want :8090", cfg.Addr)
 	}
 	if cfg.KeycloakIssuer == "" {
 		t.Error("KeycloakIssuer is empty; expected a default")