Add favorite notes sorting to display starred notes at top

- Favorited/starred notes now appear at the top of the notes list
- Within each group (favorites/non-favorites), notes are sorted by modified date (newest first)
- Matches mobile app behavior

src/App.tsx

@@ -315,6 +315,12 @@ function App() {
              note.content.toLowerCase().includes(search);
     }
     return true;
+  }).sort((a, b) => {
+    // Sort favorites first, then by modified date (newest first)
+    if (a.favorite !== b.favorite) {
+      return a.favorite ? -1 : 1;
+    }
+    return b.modified - a.modified;
   });
 
   const selectedNote = notes.find(n => n.id === selectedNoteId) || null;