fix: print PagedJS content via new window

Open iframe content in a new window for printing to avoid
blank page issues with srcdoc iframes. The window opens,
prints, then closes automatically.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/App.vue

@@ -279,8 +279,28 @@ const handlePrint = (event) => {
   if ((event.metaKey || event.ctrlKey) && event.key === 'p') {
     event.preventDefault();
     const frame = activeFrame.value;
-    if (frame && frame.contentWindow) {
-      frame.contentWindow.print();
+    if (frame && frame.contentDocument) {
+      // Get the full HTML content of the iframe
+      const content = frame.contentDocument.documentElement.outerHTML;
+
+      // Open a new window with the content
+      const printWindow = window.open('', '_blank');
+      printWindow.document.write(content);
+      printWindow.document.close();
+
+      // Wait for content to load then print
+      printWindow.onload = () => {
+        printWindow.print();
+        printWindow.close();
+      };
+
+      // Fallback if onload doesn't fire
+      setTimeout(() => {
+        if (!printWindow.closed) {
+          printWindow.print();
+          printWindow.close();
+        }
+      }, 500);
     }
   }
 };