Fix empty titles in Markdown/Quarto file outline

The outline entries showed up at the right lines and jumped correctly,
but their titles were blank. The text-extraction walked the heading
node's children and collected non-HeaderMark child text — but in the
Lezer Markdown grammar a heading has NO child node for its text; the
only children are the HeaderMark nodes. The title text lives in the
gaps between marks, so the walk collected nothing.

Slice the whole heading's source instead and strip the markers:
leading/trailing '#'s for ATX headings and the '==='/'---' underline
for Setext headings.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/web/frontend/js/features/source-editor/languages/markdown/document-outline.ts

@@ -33,21 +33,23 @@ const enterMarkdownNode = (
     return
   }
 
-  // Collect heading text, skipping the HeaderMark (the leading # characters)
-  let title = ''
-  const cursor = node.node.cursor()
-  if (cursor.firstChild()) {
-    do {
-      if (cursor.name !== 'HeaderMark') {
-        title += state.sliceDoc(cursor.from, cursor.to)
-      }
-    } while (cursor.nextSibling())
-  }
+  // In the Lezer Markdown grammar the heading text is NOT a child node —
+  // the only children are HeaderMark nodes ('#'s for ATX, the '='/'-'
+  // underline for Setext). The title text sits in the gaps between marks.
+  // So we slice the whole heading and strip the marker characters:
+  //  - ATX:    leading '#'s and any optional trailing '#'s
+  //  - Setext: the trailing underline line ('===' / '---')
+  const raw = state.sliceDoc(node.from, node.to)
+  const title = raw
+    .replace(/^\s*#+\s*/, '') // ATX: leading ### markers
+    .replace(/\s*#+\s*$/, '') // ATX: optional closing ### markers
+    .replace(/\n[=-]+\s*$/, '') // Setext: underline line
+    .trim()
 
   items.push({
     line: state.doc.lineAt(node.from).number,
     toLine: state.doc.lineAt(node.to).number,
-    title: title.trim(),
+    title,
     from: node.from,
     to: node.to,
     level,