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/modules/components/img-popup.js

@@ -4,7 +4,6 @@
  * Dependencies: https://github.com/biati-digital/glightbox
  */
 
-const html = document.documentElement;
 const lightImages = '.popup:not(.dark)';
 const darkImages = '.popup:not(.light)';
 let selector = lightImages;
@@ -33,26 +32,17 @@ export function imgPopup() {
     document.querySelector('.popup.dark') === null
   );
 
-  if (
-    (html.hasAttribute('data-mode') &&
-      html.getAttribute('data-mode') === 'dark') ||
-    (!html.hasAttribute('data-mode') &&
-      window.matchMedia('(prefers-color-scheme: dark)').matches)
-  ) {
+  if (Theme.visualState === Theme.DARK) {
     selector = darkImages;
   }
 
   let current = GLightbox({ selector: `${selector}` });
 
-  if (hasDualImages && document.getElementById('mode-toggle')) {
+  if (hasDualImages && Theme.switchable) {
     let reverse = null;
 
     window.addEventListener('message', (event) => {
-      if (
-        event.source === window &&
-        event.data &&
-        event.data.direction === ModeToggle.ID
-      ) {
+      if (event.source === window && event.data && event.data.id === Theme.ID) {
         updateImages(current, reverse);
       }
     });