Optional Share Temporary Preview action for HTML exports

Is your feature request related to a problem? Please describe.

VNote can export a note or notebook as browser-ready HTML, but sharing that result for short-lived review still requires the user to configure hosting, send an archive, or use a permanent publishing workflow. This adds friction when the goal is simply to let someone open the rendered result in a browser and review it.

Describe the solution you'd like

Add an optional Share Temporary Preview action alongside the existing HTML export flow.

The action could:

1. Reuse VNote's existing HTML export pipeline rather than introducing another Markdown renderer.
2. Upload the generated HTML and all referenced exported assets to temp.md.
3. Return a temporary, unlisted URL that VNote can copy or open.
4. Allow a later export to update the same URL, or let the user create a new preview.
5. Show the preview's status and expiration, with an option to revoke it permanently.

This should be explicitly opt-in and separate from local HTML/PDF export. Before uploading, the UI should clearly state that anyone with the URL can view it, that it is unlisted rather than private, and that it expires. Any update/revoke capability returned by the service should be treated as a secret and never written into the note or exported bundle.

temp.md accepts static files or directories, keeps one URL stable across updates, reports lifecycle state and expiration, and supports permanent revocation: https://temp.md/docs

Describe alternatives you've considered

• Continue exporting HTML and require users to configure a separate host.
• Send the exported directory or archive directly, which is less convenient for browser review and makes revisions harder to track.
• Use a permanent publishing provider, which is a larger ownership and configuration commitment than a disposable preview.

Additional context

I work on temp.md and am happy to prepare a focused PR if this direction fits VNote. I would keep the integration isolated from the current export behavior and include tests for asset collection, failed uploads, updating an existing URL, and revocation.

Start with VNote's existing HTML export flow and the temp.md documentation linked in the issue; identify the export entry point and asset collection path. Review the proposed tests for asset collection, failed uploads, stable-URL updates, and revocation. Done means the opt-in action supports temporary previews without changing local export behavior and keeps service secrets out of notes and bundles.