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/vitest.config.ts

@@ -0,0 +1,9 @@
+import path from "node:path";
+import { mergeConfig } from "vitest/config";
+import { jsdomVitestConfig } from "@repo/core-typescript/vitest.base.jsdom";
+
+export default mergeConfig(jsdomVitestConfig, {
+  resolve: {
+    alias: { "@": path.resolve(__dirname, "./src") },
+  },
+});