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/plugins/global/scheduled-publisher.php

@@ -0,0 +1,24 @@
+<?php
+/**
+ * Scheduled Publisher Plugin
+ *
+ * Publishes due scheduled posts created via /publiser. Runs on every page
+ * request (piggybacking on normal site traffic) instead of relying on a
+ * cron job - there's nothing to configure on the host, and with regular
+ * traffic a scheduled post goes live within moments of its scheduled time.
+ *
+ * Usage: add to custom/config.ini:
+ *   [plugins]
+ *   enabled = "languages, scheduled-publisher"
+ */
+
+require_once __DIR__ . '/../publiser-lib.php';
+
+Hooks::add(Hook::CONTEXT_READY, function (Context $ctx, array $config) {
+    try {
+        publiserPublishDueScheduledItems();
+    } catch (Throwable $e) {
+        error_log('scheduled-publisher: ' . $e->getMessage());
+    }
+    return $ctx;
+});