Initialize Black 7 PWA with React, Vite, and app icons

Sets up Vite + React + TypeScript with vite-plugin-pwa for offline support.
Adds app icon (line-drawn 7 on black) in all required sizes with a generation script.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/App.tsx

@@ -0,0 +1,7 @@
+export default function App() {
+  return (
+    <div>
+      <h1>Black 7</h1>
+    </div>
+  )
+}

src/main.tsx

@@ -0,0 +1,9 @@
+import { StrictMode } from 'react'
+import { createRoot } from 'react-dom/client'
+import App from './App'
+
+createRoot(document.getElementById('root')!).render(
+  <StrictMode>
+    <App />
+  </StrictMode>
+)