feat(core-ui): add jsdom Vitest config + RTL tests for components

Adopts jsdomVitestConfig from @repo/core-typescript. Adds
@testing-library/react, @testing-library/user-event, jsdom devDeps.
Writes smoke + interaction tests for every atom/molecule/organism/template
using renderWithProviders from @repo/core-testing/react.

Components covered:
- atoms: Button (5 tests), Input (4), Label (2)
- molecules: FormField (5)
- organisms / templates: empty barrels, no components

Adjustments:
- core-ui/tsconfig.json now extends react-library.json (jsx: react-jsx)
  with rootDir "." + paths {"@/*"} + types [vitest/globals, jest-dom]
- core-typescript/vitest.base.jsdom.ts uses ./vitest.base.node.ts (explicit
  .ts extension) so Node's ESM resolver finds the source file when loaded
  via the package export from a downstream package

Spec: §6.1, §6.5

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/core-ui/src/atoms/label/label.test.tsx

@@ -0,0 +1,16 @@
+import { describe, it, expect } from "vitest";
+import { renderWithProviders } from "@repo/core-testing/react";
+import { screen } from "@testing-library/react";
+import { Label } from "./label";
+
+describe("Label", () => {
+  it("renders the label text", () => {
+    renderWithProviders(<Label htmlFor="email">Email</Label>);
+    expect(screen.getByText("Email")).toBeInTheDocument();
+  });
+
+  it("forwards htmlFor to associate with an input", () => {
+    renderWithProviders(<Label htmlFor="email">Email</Label>);
+    expect(screen.getByText("Email")).toHaveAttribute("for", "email");
+  });
+});