feat(renderer): PrintPreview overlay + App.tsx mount

src/renderer/App.tsx

@@ -1,15 +1,28 @@
+import { useState, useEffect } from 'react';
 import { AppShell } from './components/layout/AppShell';
 import { ModalLayer } from './components/modals/ModalLayer';
 import { Toaster } from './components/ui/sonner';
+import { ReplPanel } from './components/tools/ReplPanel';
+import { PrintPreview } from './components/tools/PrintPreview';
 import { useWelcomeTrigger } from './hooks/use-welcome-trigger';
 
 function App() {
   useWelcomeTrigger();
+  const [printOpen, setPrintOpen] = useState(false);
+
+  useEffect(() => {
+    const handler = () => setPrintOpen(true);
+    window.addEventListener('mc:print', handler);
+    return () => window.removeEventListener('mc:print', handler);
+  }, []);
+
   return (
     <>
       <AppShell />
       <ModalLayer />
       <Toaster />
+      <ReplPanel />
+      {printOpen && <PrintPreview onClose={() => setPrintOpen(false)} />}
     </>
   );
 }