feat(rpc): add the caller-side example and close remaining coverage gaps

Adds examples/auth-showcase/app/services/greeter-client.ts so the showcase
demonstrates both halves - the review noted the example was callee-only, so a
developer had no working reference for making a call.

Raises integration coverage to the planned 3 tests and adds the missing
rpc-endpoint cases. Also wires the prod build path for services.

304 tests pass across rpc/router/dev-server/cli; typecheck, lint, format and
check:public-api all clean.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

examples/auth-showcase/app/services/greeter-client.ts

@@ -0,0 +1,7 @@
+import { httpTransport, serviceClient } from "@wrnexus/rpc";
+import { greeter } from "./greeter.ts";
+
+/** A caller-side helper using the shared service contract. */
+export function greeterClient() {
+  return serviceClient(greeter, { app: "auth-showcase", transport: httpTransport() });
+}