feat: add keyboard shortcuts for notes, the note list and the app

lib/markdown_editing.dart

@@ -110,7 +110,7 @@ class MarkdownController extends TextEditingController {
     _updateMatches();
   }
 
-  final Map<String, TextStyle> theme;
+  Map<String, TextStyle> theme;
 
   List<String> _terms = const [];
   List<TextRange> _matches = const [];
@@ -375,3 +375,40 @@ TextEditingValue indentLines(TextEditingValue value, {bool outdent = false}) {
     ),
   );
 }
+
+/// Toggles emphasis [marker] (`*` or `**`) around the selection, leaving the
+/// selection on the same text. With nothing selected, inserts an empty pair.
+TextEditingValue toggleEmphasis(TextEditingValue value, String marker) {
+  final sel = value.selection;
+  if (!sel.isValid) return value;
+  final text = value.text;
+  final s = sel.start;
+  final e = sel.end;
+  final char = marker[0];
+
+  var before = 0;
+  while (before < s && text[s - before - 1] == char) {
+    before++;
+  }
+  var after = 0;
+  while (e + after < text.length && text[e + after] == char) {
+    after++;
+  }
+  // A run of 3 is bold plus italic, so either marker can be removed from it.
+  final run = before < after ? before : after;
+  final present = marker.length == 2 ? run >= 2 : run == 1 || run == 3;
+
+  final len = marker.length;
+  if (present) {
+    return TextEditingValue(
+      text: text.replaceRange(e, e + len, '').replaceRange(s - len, s, ''),
+      selection: TextSelection(
+          baseOffset: sel.baseOffset - len, extentOffset: sel.extentOffset - len),
+    );
+  }
+  return TextEditingValue(
+    text: text.replaceRange(s, e, '$marker${text.substring(s, e)}$marker'),
+    selection: TextSelection(
+        baseOffset: sel.baseOffset + len, extentOffset: sel.extentOffset + len),
+  );
+}