test: Vitest + RTL component tests with mocked Wails bindings

- vitest + jsdom + @testing-library/react setup
- mocked wailsjs/go/main/MatrixService + runtime
- tests for: LoginScreen, App routing, HomeScreen auto-relogin,
  RoomList, Composer, EventBubble
- pnpm test runs the suite

Frontend coverage for matrix_client_pc (flow 0010 PC client).

frontend/vitest.config.ts

@@ -0,0 +1,13 @@
+import { defineConfig } from "vitest/config";
+import react from "@vitejs/plugin-react";
+
+export default defineConfig({
+  plugins: [react()],
+  test: {
+    environment: "jsdom",
+    globals: true,
+    setupFiles: ["./src/test/setup.ts"],
+    css: false,
+    include: ["src/__tests__/**/*.test.{ts,tsx}"],
+  },
+});