fix(chart): convert markdown to HTML for TipTap insertion

- Convert chart markdown to <pre><code class="language-chart"> HTML format
- Fix parseHTML to store code content in node attrs
- Fix renderHTML to output actual code content instead of placeholder

This fixes charts rendering as raw markdown text instead of visual charts.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

memento-note/components/tiptap-chart-extension.tsx

@@ -70,7 +70,12 @@ export const ChartExtension = Node.create({
 
           // Detect chart blocks by class="language-chart"
           if (codeEl && codeEl.classList.contains('language-chart')) {
-            return {}
+            // Store the code content as an attribute
+            const codeContent = codeEl.textContent || ''
+            return {
+              code: codeContent,
+              language: 'chart'
+            }
           }
 
           return false
@@ -79,8 +84,10 @@ export const ChartExtension = Node.create({
     ]
   },
 
-  renderHTML({ HTMLAttributes }) {
-    return ['pre', { ...HTMLAttributes, class: 'language-chart' }, ['code', { class: 'language-chart' }, 0]]
+  renderHTML({ HTMLAttributes, node }) {
+    // Get the code content from node attrs
+    const code = node.attrs.code || ''
+    return ['pre', { ...HTMLAttributes, class: 'language-chart' }, ['code', { class: 'language-chart' }, code]]
   },
 
   addNodeView() {