chore: scaffold @insignia/iios-messaging-ui with jsdom test setup

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

packages/iios-messaging-ui/vitest.config.ts

@@ -0,0 +1,13 @@
+import { defineConfig } from 'vitest/config';
+
+// This package owns its vitest config on purpose. The ROOT config includes only
+// `.ts` (never `.tsx`) and provisions a Postgres DB via globalSetup for every run —
+// a pure-UI package must not drag a database along, and its tests are .tsx.
+export default defineConfig({
+  test: {
+    environment: 'jsdom',
+    include: ['src/**/*.{test,spec}.{ts,tsx}'],
+    setupFiles: ['./src/test-setup.ts'],
+    globals: false,
+  },
+});