ContentAPI voor PHP content bestanden + handleiding in admin

- Nieuwe ContentAPI class beschikbaar als $api in PHP content bestanden
  met methodes: getAllPages, getPage, getMenu, getConfig, buildUrl, etc.
- Admin handleiding pagina op /admin/guide met taalwisselaar
- Zijbalk link naar handleiding in admin menu
- Dubbele alert in config pagina verwijderd
- Handleidingen (nl/en) uitgebreid met Content API referentie

cms/core/class/CodePressCMS.php

@@ -783,7 +783,8 @@ class CodePressCMS {
         $title = $metadata['title'] ?? '';
         
         ob_start();
-        // Make metadata available to the included file
+        // Make API and metadata available to the included file
+        $api = new ContentAPI($this);
         $pageMetadata = $metadata;
         include $filePath;
         $content = ob_get_clean();
@@ -1011,7 +1012,6 @@ class CodePressCMS {
         $this->pluginManager->doAction('onBeforeRender');
         
         $menu = $this->getMenu();
-        $breadcrumb = $this->generateBreadcrumb();
         
         // Get homepage title
         $homepageTitle = $this->getHomepageTitle();
@@ -1026,6 +1026,10 @@ class CodePressCMS {
         // Get layout from page metadata
         $layout = $page['layout'] ?? 'sidebar-content';
         
+        // Determine if sidebar toggle should be shown
+        $hasSidebar = $layout !== 'content' && !empty(trim($sidebarContent));
+        $breadcrumb = $this->generateBreadcrumb($hasSidebar);
+        
         // Prepare template data
         $templateData = [
             'site_title' => $this->config['site_title'],
@@ -1154,11 +1158,15 @@ class CodePressCMS {
     /**
      * Generate breadcrumb navigation HTML
      * 
+     * @param bool $hasSidebar Whether sidebar content exists and should show toggle
      * @return string Breadcrumb HTML
      */
-    public function generateBreadcrumb() {
+    public function generateBreadcrumb($hasSidebar = true) {
         // Sidebar toggle button (shown before home icon in breadcrumb)
-        $sidebarToggle = '<li class="breadcrumb-item sidebar-toggle-item"><button type="button" class="sidebar-toggle-btn" onclick="toggleSidebar()" title="Toggle Sidebar" aria-label="Toggle Sidebar" aria-expanded="true"><i class="bi bi-layout-sidebar-inset"></i></button></li>';
+        $sidebarToggle = '';
+        if ($hasSidebar) {
+            $sidebarToggle = '<li class="breadcrumb-item sidebar-toggle-item"><button type="button" class="sidebar-toggle-btn" onclick="toggleSidebar()" title="Toggle Sidebar" aria-label="Toggle Sidebar" aria-expanded="true"><i class="bi bi-layout-sidebar-inset"></i></button></li>';
+        }
         
         if (isset($_GET['search'])) {
             return '<nav aria-label="breadcrumb"><ol class="breadcrumb">' . $sidebarToggle . '<li class="breadcrumb-item"><a href="/' . $this->currentLanguage . '"><i class="bi bi-house"></i></a></li><li class="breadcrumb-item"> > </li><li class="breadcrumb-item active">' . $this->t('search') . '</li></ol></nav>';