Add Custom Pages Functionality to Serve Custom Text at /page-name/

[coignard]

Currently, Weblog does not support serving custom static pages at specific URLs like /page-name/. Adding this functionality would allow for custom text content to be displayed at specified URL paths, making the system more versatile and useful for various custom content needs.

/pages/
    - about.txt → /about/
    - contact.txt → /contact/
    - ...

In case of a conflict with a post slug, the custom page should take priority and be rendered instead of the post.