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/admin-beheerder/beveiliging.md

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+# Security
+
+## Bot protection
+
+- **BotGuard** - Bot/AI detection
+- **Rate limiting** - Limit requests per IP
+- **Block/allowlist** - Block or allow IPs
+
+## Session settings
+
+- **Session timeout** - Default 3600 seconds
+- **Max login attempts** - Default 5 attempts

guide/en/admin-beheerder/configuratie.md

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+# Configuration
+
+## General settings
+
+- **Site title** - Website name
+- **Default language** - nl/en/de/fr
+- **Author** - Name and email
+- **Analytics** - Visitor tracking on/off
+- **Logging** - Log files on/off

guide/en/admin-beheerder/content-beheer.md

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+# Content management
+
+## Managing files
+
+- **Upload** - Upload media files
+- **New folder** - Create folder structure
+- **New file** - Create a page
+- **Edit** - Modify existing content
+- **Rename** - Change file names
+- **Move** - Move content
+- **Delete** - Remove content
+
+## Editor
+
+- CodeMirror with syntax highlighting
+- Toolbar for Markdown formatting
+- Shortcuts: Ctrl+S (save), Ctrl+N (new)

guide/en/admin-beheerder/dashboard.md

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+# Dashboard
+
+The dashboard shows an overview of:
+
+- Views (30 days)
+- Unique visitors
+- Number of pages and folders
+- Active plugins
+- Recent activity
+- Quick actions

guide/en/admin-beheerder/gebruikers.md

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+# Users
+
+## Add user
+
+1. Go to **Users**
+2. Enter username
+3. Choose password
+4. Click **Add**
+
+## Delete user
+
+- Cannot delete own account
+- Confirm with password

guide/en/admin-beheerder/logs.md

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+# Logs
+
+## Log types
+
+- **Admin** - Admin actions
+- **Requests** - Website visits
+
+## Filter
+
+- Search by IP, message
+- Filter by level (info, warning, error)
+- Download as file

guide/en/admin-beheerder/plugins.md

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+# Plugins
+
+## Managing plugins
+
+- **Enable/Disable** - Turn plugins on/off
+- **Edit** - Modify plugin code
+- **Configuration** - Plugin settings
+- **Delete** - Remove plugin
+
+## New plugin
+
+1. Go to **Plugins** → **New plugin**
+2. Enter a name (e.g. `MyPlugin`)
+3. Edit `plugin.php`
+4. Enable the plugin

guide/en/admin-beheerder/statistieken.md

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+# Statistics
+
+## Overview
+
+- Total views
+- Unique visitors
+- Countries with flags
+- Top pages
+- Referrers
+
+## Filters
+
+- Period: 7/30/90 days or all
+- Export: CSV or JSON

guide/en/admin-beheerder/thema-beheer.md

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+# Theme management
+
+## Managing themes
+
+1. Go to **Theme** in admin menu
+2. **Activate** - Choose active theme
+3. **Compile SCSS** - Process SCSS to CSS
+4. **New theme** - Create custom theme
+
+## Theme structure
+
+```
+themes/default/
+├── theme.json          # Theme configuration
+├── base.twig           # Main layout
+├── full_content.twig   # Layouts
+├── left_sidebar.twig
+├── right_sidebar.twig
+├── partials/           # Header, nav, footer
+└── assets/             # CSS, JS, images
+```