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.

compose.yaml

@@ -10,4 +10,4 @@ services:
     ports:
       - "4040:80"
     command: >
-      bash -c "chown -R www-data:www-data /var/www/custom/data /var/www/custom/assets && apache2-foreground"
+      bash -c "chown -R www-data:www-data /var/www/custom/data /var/www/custom/assets /var/www/html/nyheter /var/www/html/artikler && apache2-foreground"