Wire up Tailwind CSS 4, Vitest, and core app libraries

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.

tsconfig.web.json

@@ -10,6 +10,10 @@
     "composite": true,
     "jsx": "react-jsx",
     "baseUrl": ".",
+    "types": [
+      "vitest/globals",
+      "@testing-library/jest-dom"
+    ],
     "paths": {
       "@renderer/*": [
         "src/renderer/src/*"