Add character count label on editor panel so users can see how much they've written

Implements Issue #99

lib/screens/editor.dart

@@ -281,6 +281,10 @@ class _EditorScreenState extends State<EditorScreen> {
                 buildVisibilitySelector(context),
                 const VerticalPadding(),
                 buildContentField(context),
+                CharacterCountWidget(
+                  contentController: contentController,
+                  linkPreviewController: linkPreviewController,
+                ),
                 const VerticalPadding(),
                 buildLinkWithPreview(context),
                 const VerticalPadding(),
@@ -694,3 +698,52 @@ class _EditorScreenState extends State<EditorScreen> {
     });
   }
 }
+
+class CharacterCountWidget extends StatefulWidget {
+  final TextEditingController contentController;
+  final TextEditingController linkPreviewController;
+
+  const CharacterCountWidget({
+    super.key,
+    required this.contentController,
+    required this.linkPreviewController,
+  });
+
+  @override
+  State<CharacterCountWidget> createState() => _CharacterCountWidgetState();
+}
+
+class _CharacterCountWidgetState extends State<CharacterCountWidget> {
+  var count = 0;
+
+  @override
+  void initState() {
+    super.initState();
+    calculateCount();
+    widget.contentController.addListener(countRefresh);
+    widget.linkPreviewController.addListener(countRefresh);
+  }
+
+  @override
+  void dispose() {
+    widget.contentController.removeListener(countRefresh);
+    widget.linkPreviewController.removeListener(countRefresh);
+    super.dispose();
+  }
+
+  void countRefresh() {
+    setState(() {
+      calculateCount();
+    });
+  }
+
+  void calculateCount() {
+    count = widget.linkPreviewController.text.length +
+        widget.contentController.text.length;
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Text('Character Count: $count');
+  }
+}