perf: speed up page rendering and jekyll build process (#2034)

- Ensure inline scripts execute after the DOM has fully loaded.
- Use Rollup to bundle the theme-mode and Mermaid scripts, reducing the number of Jekyll include snippets.

_javascript/page.js

@@ -1,9 +1,15 @@
 import { basic, initSidebar, initTopbar } from './modules/layouts';
-import { loadImg, imgPopup, initClipboard } from './modules/plugins';
+import {
+  loadImg,
+  imgPopup,
+  initClipboard,
+  loadMermaid
+} from './modules/components';
 
 loadImg();
 imgPopup();
 initSidebar();
 initTopbar();
 initClipboard();
+loadMermaid();
 basic();