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.
Add firefox and webkit projects alongside chromium (desktop/mobile),
and enable reuseExistingServer so the fixture server isn't restarted
per run. Chromium/Firefox/WebKit browsers installed via
npx playwright install.