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/rich-text-editor.tsx

@@ -295,7 +295,17 @@ export const RichTextEditor = forwardRef<RichTextEditorHandle, RichTextEditorPro
       if (!editor || !editor.isEditable) return
 
       try {
-        // Insert the chart markdown at current position
+        // Convert markdown chart to HTML format for TipTap
+        // Input: ```chart\nbar\nTitle\nlabel: value\n```
+        // Output: <pre><code class="language-chart">bar\nTitle\nlabel: value</code></pre>
+        const chartContent = markdown
+          .replace(/```chart\n?/gi, '')
+          .replace(/```$/gi, '')
+          .trim()
+
+        const htmlContent = `<pre><code class="language-chart">${chartContent}</code></pre>`
+
+        // Insert the chart HTML at current position
         const { from } = editor.state.selection
 
         // Check if we're in the middle of text, if so create a new paragraph
@@ -311,8 +321,8 @@ export const RichTextEditor = forwardRef<RichTextEditorHandle, RichTextEditorPro
           }
         }
 
-        // Insert the chart
-        editor.chain().focus().insertContent(markdown).run()
+        // Insert the chart as HTML (not markdown)
+        editor.chain().focus().insertContent(htmlContent).run()
       } catch (error) {
         console.error('[handleSelectChart] Failed to insert chart:', error)
         toast.error('Failed to insert chart. Please try again.')