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/lib/ai/services/agent-executor.service.ts

@@ -43,13 +43,12 @@ async function createAgentNote(data: {
   notebookId: string | null
   autoGenerated?: boolean
 }) {
-  const htmlContent = markdownToHtml(data.content)
   return prisma.note.create({
     data: {
       title: data.title,
-      content: htmlContent,
-      type: 'richtext',
-      isMarkdown: false,
+      content: data.content,
+      type: 'markdown',
+      isMarkdown: true,
       autoGenerated: data.autoGenerated ?? true,
       userId: data.userId,
       notebookId: data.notebookId,

memento-note/lib/ai/tools/note-crud.tool.ts

@@ -51,13 +51,12 @@ toolRegistry.register({
       }),
       execute: async ({ title, content, notebookId, images }) => {
         try {
-          const htmlContent = markdownToHtml(content)
           const note = await prisma.note.create({
             data: {
               title,
-              content: htmlContent,
-              type: 'richtext',
-              isMarkdown: false,
+              content,
+              type: 'markdown',
+              isMarkdown: true,
               autoGenerated: true,
               userId: ctx.userId,
               notebookId: notebookId || null,