Add "Created At" / "Last Updated" metadata to Markdown export

Currently, the app tracks both the "Created At" and "Last Updated" timestamps for each note, as visible in the Stats panel. However, this metadata is not included in the Markdown file when exporting notes—either manually or through scheduled exports. For users who ingest Markdown exports into external systems (e.g. a personal knowledge base), having access to this temporal metadata is crucial for organizing and tracking content chronologically.

Please consider adding an option to include the Created At and Last Updated timestamps to the exported .md files. Maybe this could be toggleable via the “Options” menu in the export settings.