fix: agent notes default to markdown, add convert-to-rich-text option

- Agent-created notes are now type 'markdown' by default (raw markdown content)
- Switching note type from markdown → richtext auto-converts content to HTML
  via /api/ai/convert-markdown endpoint using the existing markdownToHtml utility
- Users can freely switch between markdown and richtext in the note type selector

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

memento-note/components/note-inline-editor.tsx

@@ -495,10 +495,36 @@ export function NoteInlineEditor({
 
           <NoteTypeSelector
             value={noteType}
-            onChange={(newType) => {
+            onChange={async (newType) => {
+              const oldType = noteType
               setNoteType(newType)
               if (newType === 'markdown') setShowMarkdownPreview(true)
               else setShowMarkdownPreview(false)
+
+              // When switching from markdown to richtext, convert content to HTML
+              if (oldType === 'markdown' && newType === 'richtext') {
+                try {
+                  const res = await fetch('/api/ai/convert-markdown', {
+                    method: 'POST',
+                    headers: { 'Content-Type': 'application/json' },
+                    body: JSON.stringify({ content }),
+                  })
+                  if (res.ok) {
+                    const { html } = await res.json()
+                    setContent(html)
+                    saveInline(note.id, {
+                      type: 'richtext',
+                      isMarkdown: false,
+                      content: html,
+                    }).catch(() => {})
+                    onChange?.(note.id, { type: 'richtext', isMarkdown: false, content: html })
+                    return
+                  }
+                } catch {
+                  // Fall through to save without conversion
+                }
+              }
+
               // Persist both type and isMarkdown immediately
               saveInline(note.id, {
                 type: newType,