Offline page redesign, remove brand showcase tab, force a11y/theme to bottom-right

- Offline page: full-viewport Joomla offline_image background, centered glass card
  overlay with logo glow, message, offline position, login accordion, copyright
- Favicon: added to offline page, HTML-escaped paths in helper
- Removed brand showcase tab, added footer CSS vars to CSS Variables tab
- Forced a11y toolbar and theme FAB to bottom-right (removed position selectors)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/helper/favicon.php

@@ -162,7 +162,7 @@ class MokoFaviconHelper
      */
     public static function getHeadTags(string $basePath): string
     {
-        $basePath = rtrim($basePath, '/');
+        $basePath = htmlspecialchars(rtrim($basePath, '/'), ENT_QUOTES, 'UTF-8');
 
         return '<link rel="apple-touch-icon" sizes="180x180" href="' . $basePath . '/apple-touch-icon.png">' . "\n"
              . '<link rel="icon" type="image/png" sizes="32x32" href="' . $basePath . '/favicon-32x32.png">' . "\n"