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/tools/set-publiser-password.php

@@ -0,0 +1,57 @@
+#!/usr/bin/env php
+<?php
+/**
+ * Set or reset the Basic Auth login for /publiser.
+ *
+ * Writes a bcrypt-hashed .htpasswd file (no dependency on the `htpasswd`
+ * binary being installed - Apache's mod_authn_file accepts $2y$ hashes).
+ *
+ * Usage:
+ *   php custom/tools/set-publiser-password.php <username> <password>
+ *   php custom/tools/set-publiser-password.php            (interactive)
+ */
+
+$htpasswdPath = dirname(__DIR__, 2) . '/content/publiser/.htpasswd';
+
+function prompt(string $question): string {
+    echo $question;
+    return trim(fgets(STDIN));
+}
+
+function promptHidden(string $question): string {
+    $isWindows = stripos(PHP_OS, 'WIN') === 0;
+    if (!$isWindows) {
+        system('stty -echo');
+    }
+    $value = prompt($question);
+    if (!$isWindows) {
+        system('stty echo');
+        echo "\n";
+    }
+    return $value;
+}
+
+$args = array_slice($argv, 1);
+
+$username = $args[0] ?? prompt('Username: ');
+$password = $args[1] ?? promptHidden('Password: ');
+
+if ($username === '' || $password === '') {
+    fwrite(STDERR, "Username and password are required.\n");
+    exit(1);
+}
+
+if (str_contains($username, ':')) {
+    fwrite(STDERR, "Username cannot contain ':'.\n");
+    exit(1);
+}
+
+$hash = password_hash($password, PASSWORD_BCRYPT);
+file_put_contents($htpasswdPath, "$username:$hash\n");
+// World-readable: the web server user (www-data, varies by host/container)
+// needs read access. This is safe - Apache denies direct HTTP access to
+// this exact filename (content/publiser/.htaccess), and reaching it any
+// other way already requires shell/filesystem access to the server.
+chmod($htpasswdPath, 0644);
+
+echo "Wrote $htpasswdPath for user \"$username\".\n";