chore: Follow up create check list UX

lib/pages/chat/chat.dart

@@ -1186,15 +1186,6 @@ class ChatController extends State<ChatPageWithRoom>
     if (choice == 'location') {
       sendLocationAction();
     }
-    if (choice == 'checklist') {
-      if (sendController.text.isEmpty) {
-        sendController.text = '- [ ] ';
-      } else {
-        sendController.text += '\n- [ ] ';
-      }
-      onInputBarChanged(sendController.text);
-      inputFocus.requestFocus();
-    }
   }
 
   unpinEvent(String eventId) async {

lib/pages/chat/chat_input_row.dart

@@ -124,18 +124,6 @@ class ChatInputRow extends StatelessWidget {
                   onSelected: controller.onAddPopupMenuButtonSelected,
                   itemBuilder: (BuildContext context) =>
                       <PopupMenuEntry<String>>[
-                    PopupMenuItem<String>(
-                      value: 'checklist',
-                      child: ListTile(
-                        leading: CircleAvatar(
-                          backgroundColor: theme.colorScheme.onPrimaryContainer,
-                          foregroundColor: theme.colorScheme.primaryContainer,
-                          child: const Icon(Icons.check_circle_outlined),
-                        ),
-                        title: Text(L10n.of(context).checkList),
-                        contentPadding: const EdgeInsets.all(0),
-                      ),
-                    ),
                     if (PlatformInfos.isMobile)
                       PopupMenuItem<String>(
                         value: 'location',

lib/utils/markdown_context_builder.dart

@@ -54,6 +54,35 @@ Widget markdownContextBuilder(
             ContextMenuController.removeAny();
           },
         ),
+        ContextMenuButtonItem(
+          label: l10n.checkList,
+          onPressed: () {
+            final text = controller.text;
+            final selection = controller.selection;
+
+            var start = selection.textBefore(text).lastIndexOf('\n');
+            if (start == -1) start = 0;
+            final end = selection.end;
+
+            final fullLineSelection =
+                TextSelection(baseOffset: start, extentOffset: end);
+
+            const checkBox = '- [ ]';
+
+            final replacedRange = fullLineSelection
+                .textInside(text)
+                .split('\n')
+                .map(
+                  (line) => line.startsWith(checkBox) || line.isEmpty
+                      ? line
+                      : '$checkBox $line',
+                )
+                .join('\n');
+            controller.text =
+                controller.text.replaceRange(start, end, replacedRange);
+            ContextMenuController.removeAny();
+          },
+        ),
         ContextMenuButtonItem(
           label: l10n.boldText,
           onPressed: () {