fix(ui): stub Node built-ins for fixture bundle

Replace platform: 'node' (incompatible with iife browser bundle) with
explicit aliases for node:async_hooks, node:crypto, node:fs/promises,
node:path pointing at e2e/ui/node-stubs.mjs. Provides shape-compatible
exports so esbuild can bundle the UI fixture without failing on Node
built-ins. Increase webServer timeout to 120s for reliable startup.

playwright.ui.config.ts

@@ -64,7 +64,7 @@ export default defineConfig({
 	webServer: {
 		command: "node e2e/ui/fixture-server.mjs",
 		url: `${baseURL}/health`,
-		timeout: 60000,
+		timeout: 120000,
 		reuseExistingServer: true,
 		env: { UI_TEST_PORT: String(port) },
 	},