Add standalone /publiser admin application

Implement a minimal, dependency-free publishing tool to manage news
and articles. The app includes:

- A Markdown-based block editor with rich-text capabilities.
- Image upload and resizing using GD.
- Support for drafts, scheduled publishing, and a trash system.
- Integrated Basic Auth protection via PHP and .htpasswd.
- A global plugin for automatic execution of scheduled posts.

The tool reuses core site logic in custom/plugins/publiser-lib.php to
ensure consistency between the editor and the live site.

custom/config.ini

@@ -3,7 +3,7 @@ default = "no"
 available = "no"
 
 [plugins]
-enabled = "languages"
+enabled = "languages, scheduled-publisher"
 
 [feed]
 exclude_files = "nyhetsbrev, newsletter"