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

themes/demo/assets/css/mobile.css

@@ -0,0 +1,54 @@
+/* Mobile search improvements */
+@media (max-width: 991.98px) {
+    .navbar {
+        position: relative;
+    }
+    
+    /* Hide desktop elements on mobile */
+    .d-none.d-lg-flex {
+        display: none !important;
+    }
+    
+    #mobileSearch {
+        position: absolute;
+        top: 100%;
+        left: 0;
+        right: 0;
+        background: var(--header-bg);
+        z-index: 1030;
+    }
+    
+    #mobileSearch.show {
+        box-shadow: 0 4px 6px rgba(0,0,0,0.1);
+    }
+    
+    /* Ensure navigation doesn't overlap with expanded search */
+    .navigation-section {
+        margin-top: 0;
+        border: none !important;
+    }
+}
+
+/* Desktop improvements */
+@media (min-width: 992px) {
+    /* Hide mobile elements on desktop */
+    .d-lg-none {
+        display: none !important;
+    }
+    
+    /* Hide mobile search on desktop */
+    #mobileSearch {
+        display: none !important;
+    }
+}
+
+/* Search form improvements */
+.form-control[type="search"] {
+    min-width: 200px;
+}
+
+@media (max-width: 576px) {
+    .form-control[type="search"] {
+        min-width: 150px;
+    }
+}

themes/demo/assets/css/style.css

@@ -0,0 +1,4 @@
+/*!
+ * Bootstrap  v5.3.8 (https://getbootstrap.com/)
+ * Copyright 2011-2025 The Bootstrap Authors
+ * Licensed under MIT (https://github.com/twbs/bootstrap/blob/main/LICENSE)