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

admin/theme/default/assets/codemirror/addon/selection/active-line.min.js

@@ -0,0 +1 @@
+!function(e){"object"==typeof exports&&"object"==typeof module?e(require("../../lib/codemirror")):"function"==typeof define&&define.amd?define(["../../lib/codemirror"],e):e(CodeMirror)}(function(i){"use strict";var a="CodeMirror-activeline",s="CodeMirror-activeline-background",c="CodeMirror-activeline-gutter";function l(e){for(var t=0;t<e.state.activeLines.length;t++)e.removeLineClass(e.state.activeLines[t],"wrap",a),e.removeLineClass(e.state.activeLines[t],"background",s),e.removeLineClass(e.state.activeLines[t],"gutter",c)}function o(t,e){for(var n=[],i=0;i<e.length;i++){var o=e[i],r=t.getOption("styleActiveLine");("object"==typeof r&&r.nonEmpty?o.anchor.line==o.head.line:o.empty())&&(r=t.getLineHandleVisualStart(o.head.line),n[n.length-1]!=r&&n.push(r))}!function(e,t){if(e.length==t.length){for(var n=0;n<e.length;n++)if(e[n]!=t[n])return;return 1}}(t.state.activeLines,n)&&t.operation(function(){l(t);for(var e=0;e<n.length;e++)t.addLineClass(n[e],"wrap",a),t.addLineClass(n[e],"background",s),t.addLineClass(n[e],"gutter",c);t.state.activeLines=n})}function r(e,t){o(e,t.ranges)}i.defineOption("styleActiveLine",!1,function(e,t,n){n=n!=i.Init&&n;t!=n&&(n&&(e.off("beforeSelectionChange",r),l(e),delete e.state.activeLines),t&&(e.state.activeLines=[],o(e,e.listSelections()),e.on("beforeSelectionChange",r)))})});