fix: re-enable boot sequence after refactor

Restore useState<Phase>('boot') in App.tsx, completing the refactoring
cycle (was temporarily set to 'pmr' for faster visual review).

src/App.tsx

@@ -45,7 +45,7 @@ function SkipButton({ onSkip }: { onSkip: () => void }) {
 }
 
 function App() {
-  const [phase, setPhase] = useState<Phase>('pmr')
+  const [phase, setPhase] = useState<Phase>('boot')
   const cursorPositionRef = useRef<{ x: number; y: number } | null>(null)
 
   useEffect(() => {