feat(core-*): add Vitest configs + composition tests

core-api: appRouter exposes all 4 feature routers + blog procedure shape.
core-cms: payloadConfig registers all collections + globals.
core-trpc: client + provider exports verified.

Spec: §6.1, §6.6

packages/core-trpc/src/client.test.ts

@@ -0,0 +1,12 @@
+import { describe, it, expect } from "vitest";
+import { useTRPC, TRPCProvider } from "./client";
+
+describe("core-trpc client exports", () => {
+  it("exports useTRPC hook", () => {
+    expect(useTRPC).toBeTypeOf("function");
+  });
+
+  it("exports TRPCProvider component", () => {
+    expect(TRPCProvider).toBeTypeOf("function");
+  });
+});