feat: Add border color support to NoteCard and DraggableNote for enhanced visual distinction

lib/widgets/note_card.dart

@@ -8,11 +8,18 @@ import 'package:notas/models/note.dart';
 // like MasonryGridView or Draggable feedback). Visual styling only.
 
 class NoteCard extends StatefulWidget {
-  const NoteCard({super.key, required this.note, this.onTap, this.isDragging = false});
+  const NoteCard({
+    super.key,
+    required this.note,
+    this.onTap,
+    this.isDragging = false,
+    this.borderColor,
+  });
 
   final Note note;
   final VoidCallback? onTap;
   final bool isDragging;
+  final Color? borderColor;
 
   @override
   State<NoteCard> createState() => _NoteCardState();
@@ -55,7 +62,10 @@ class _NoteCardState extends State<NoteCard> {
           decoration: BoxDecoration(
             color: const Color.fromRGBO(24, 25, 26, 1),
             borderRadius: BorderRadius.circular(12),
-            border: Border.all(color: Colors.white24, width: 1),
+            border: Border.all(
+              color: widget.borderColor ?? Colors.white24,
+              width: 1,
+            ),
           ),
           child: LayoutBuilder(
             builder: (BuildContext context, BoxConstraints constraints) {