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/publiser/.htaccess

@@ -0,0 +1,15 @@
+DirectorySlash On
+
+# Auth is checked in PHP (index.php), not via Apache AuthUserFile: relative
+# AuthUserFile paths resolve against ServerRoot, not this directory, and
+# that differs per environment (podman dev container vs cPanel). Some SAPIs
+# (LSAPI/CGI/FastCGI, used on cPanel) strip the Authorization header from
+# PHP by default, so forward it explicitly via an internal env var.
+<IfModule mod_rewrite.c>
+    RewriteEngine On
+    RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
+</IfModule>
+
+<Files ".htpasswd">
+    Require all denied
+</Files>