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.

content/.htaccess

@@ -2,8 +2,8 @@ DirectorySlash Off
 
 # Block direct access to content source files
 <FilesMatch "\.(ini|md|html|php)$">
-    # Allow only the entry point
-    <If "%{REQUEST_URI} != '/index.php'">
+    # Allow only the entry point, and the standalone /publiser admin app
+    <If "%{REQUEST_URI} != '/index.php' && %{REQUEST_URI} !~ m#^/publiser(/|$)#">
         Require all denied
     </If>
 </FilesMatch>
@@ -30,6 +30,13 @@ DirectorySlash Off
     RewriteCond %{REQUEST_URI} ^/app/
     RewriteRule ^(.*)$ /index.php [L,QSA]
 
+    # Standalone /publiser admin app - bypass the CMS entirely, dispatch
+    # everything to its own entry point (static assets like .css/.js are
+    # excluded so Apache serves those files directly)
+    RewriteCond %{REQUEST_URI} ^/publiser
+    RewriteCond %{REQUEST_URI} !\.(css|js|png|jpe?g|webp|gif|svg)$
+    RewriteRule ^publiser(/.*)?$ publiser/index.php [L,QSA]
+
     # Don't rewrite if file exists
     RewriteCond %{REQUEST_FILENAME} !-f
     RewriteRule ^(.*)$ /index.php [L,QSA]