feat(core-trpc): scaffold tRPC client with React Query providers

- createTRPCContext + useTRPC hook for typed client access
- NextTrpcProvider with SSR-safe absolute URL resolution
- TanstackTrpcProvider for TanStack Start apps
- /api/trpc catch-all route handler in web-next
- Wire NextTrpcProvider into app providers
- Add @repo/core-trpc to transpilePackages

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");
+  });
+});