v2.5.1: Admin theme refactor, Navigation plugin, user roles, guide restructure

- Reorganize admin into admin/theme/default/ (views + assets)
- Rename GuideNav to Navigation plugin (essential, protected)
- Plugin assets support (SCSS/CSS) loaded after theme CSS
- User roles: Admin, Content Manager, BI Manager, Site Admin
- Role-based access control (RBAC) for admin routes and sidebar
- Guide restructure: sub-topics in separate folders with sidebar nav
- Dynamic breadcrumb for homepage and subdirectories
- Fix theme path traversal (../../ -> ../) in admin.php
- Fix CodeMirror mode load order (xml -> css -> js -> htmlmixed -> php)
- Fix editor-toolbar.js null checks for plugin edit pages
- Layout select from theme.json with live frontmatter update
- Footer sticky at bottom of viewport (min-height: 100vh)
- Breadcrumb color fix (var(--nav-font) -> var(--header-bg))
- Remove language switcher from guide pages
- Update README.md and README.en.md
- Bump version to 2.5.1

guide/en/codepress-developer/architectuur.md

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+# CMS Architecture
+
+```
+codepress/
+├── cms/core/           # Core engine
+├── admin/              # Admin console
+├── themes/             # Themes
+├── plugins/            # Plugins
+├── content/            # Content
+└── public/             # Web root
+```

guide/en/codepress-developer/beveiliging.md

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+# Security
+
+## XSS prevention
+
+```php
+// Always escape
+echo htmlspecialchars($userInput, ENT_QUOTES, 'UTF-8');
+
+// In Twig (automatic)
+{{ userVariable }}
+```
+
+## CSRF tokens
+
+```php
+// Generate
+$csrf = $auth->getCsrfToken();
+
+// Verify
+if (!$auth->verifyCsrf($_POST['csrf_token'])) {
+    die('Invalid CSRF token');
+}
+```
+
+## Path traversal prevention
+
+```php
+// Use realpath() and check prefix
+$realPath = realpath($filePath);
+$realContentDir = realpath($contentDir);
+if (strpos($realPath, $realContentDir) !== 0) {
+    die('Invalid path');
+}
+```

guide/en/codepress-developer/core-classes.md

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+# Core Classes
+
+## CodePressCMS.php
+
+Main CMS class in `cms/core/class/CodePressCMS.php`:
+
+```php
+$cms = new CodePressCMS();
+$cms->init();
+$cms->renderPage($pagePath);
+```
+
+## ThemeManager.php
+
+Theme management in `cms/core/class/ThemeManager.php`:
+
+```php
+$themeManager = new ThemeManager($config);
+$themeManager->getActiveTheme();
+$themeManager->renderTwig($template, $data);
+$themeManager->compileCss($force);
+```
+
+## PluginManager.php
+
+Plugin system in `cms/core/class/PluginManager.php`:
+
+```php
+$pluginManager = new PluginManager();
+$pluginManager->loadPlugins($enabledPlugins);
+$pluginManager->executeHook($name, $params);
+```

guide/en/codepress-developer/debugging.md

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+# Debugging
+
+## Logging
+
+```php
+// Admin logging
+adminLog($config, 'info', 'Message text');
+
+// LogManager
+LogManager::log(LogManager::EVENT_ADMIN, 'info', 'Message');
+```
+
+## Disabling cache
+
+In `config.json`:
+
+```json
+{
+  "cache": {
+    "enabled": false
+  }
+}
+```

guide/en/codepress-developer/performance.md

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+# Performance
+
+## Enabling OPcache
+
+In `php.ini`:
+
+```ini
+opcache.enable=1
+opcache.memory_consumption=128
+opcache.max_accelerated_files=10000
+```
+
+## SCSS caching
+
+SCSS is compiled with caching:
+
+```php
+$themeManager->compileCss(false); // Use cache when possible
+```

guide/en/codepress-developer/plugin-development.md

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+# Plugin Development
+
+## Plugin structure
+
+```
+plugins/MyPlugin/
+├── plugin.json         # Plugin metadata
+├── plugin.php          # Plugin code
+└── config.json         # Optional configuration
+```
+
+## plugin.json
+
+```json
+{
+  "name": "My Plugin",
+  "version": "1.0.0",
+  "author": "Your Name",
+  "description": "Description"
+}
+```
+
+## plugin.php example
+
+```php
+<?php
+/**
+ * Plugin: MyPlugin
+ */
+
+echo '<div class="my-plugin">Hello World</div>';
+```
+
+## Using CMSAPI
+
+```php
+<?php
+require_once '../../cms/core/class/PluginManager.php';
+
+$api = PluginManager::getAPI();
+$config = $api->getConfig();
+$content = $api->getContent();
+```

guide/en/codepress-developer/routing.md

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+# Routing
+
+## Frontend routing
+
+Via `cms/router.php` for PHP dev server:
+
+```php
+// Clean URLs: /nl/page
+// Query: ?page=page&lang=nl
+```
+
+## Admin routing
+
+Via `public/admin.php`:
+
+```php
+// Routes: /admin/dashboard, /admin/content, etc.
+// Query parameter: ?route=dashboard
+```

guide/en/codepress-developer/testing.md

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+# Testing
+
+## Penetration tests
+
+```bash
+cd cli/test/pentest
+./security-test.sh
+```
+
+## Accessibility tests
+
+```bash
+cd cli/test
+./accessibility.sh
+```
+
+## Functional tests
+
+```bash
+cd cli/test/functional
+./content-tests.sh
+```