Add Tailwind (via Vite plugin), Vitest+RTL test setup, and the
Zustand/TanStack Query/Lucide libraries the architecture plan calls
for. Strip the electron-vite demo boilerplate (logo, IPC ping demo,
Versions component) in favor of a minimal placeholder screen.
Verified: typecheck, lint, and test suite all pass; pnpm dev boots
and serves the correct renderer HTML.
