Support Multi-User Independent Editing and Rendering of Markdown Files

[BugManL]

Description:
Currently, Slidev is designed to generate a unified slideshow from a single Markdown file. However, in some scenarios, we would like to allow different users to independently edit and render their own Markdown files, generating separate slideshows. Similar to Marp's localized usage, each user can work on their own content without interfering with others.

Feature Request:

Allow dynamically loading different Markdown files via configuration or URL parameters.
Support selecting different entry files within the same instance based on user identifiers (e.g., URL parameters, cookies).
Alternatively, provide better multi-instance support, enabling different users to run separate slideshows on different ports.
Optionally, expose a simple API that allows the backend to return the appropriate Markdown content based on user requests, making it easier to integrate with existing collaboration tools.
Use Cases:

Educational scenarios where students can independently view and edit their own slide content.
Team collaboration where each member can preview, edit, and share their own version separately.
Personal use without version conflicts, allowing users to customize their own presentations freely.
Expected Outcome:
By implementing this feature, Slidev would be more flexible in handling multi-user editing needs, allowing users to customize their slideshows dynamically rather than presenting a single, unified set of content.

Thank you for maintaining and improving Slidev! I hope you will consider this feature request. Looking forward to your response!