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.

package.json

@@ -30,6 +30,7 @@
   "devDependencies": {
     "@babel/core": "^7.25.2",
     "@babel/plugin-transform-class-properties": "^7.25.4",
+    "@babel/plugin-transform-private-methods": "^7.25.7",
     "@babel/preset-env": "^7.25.4",
     "@commitlint/cli": "^19.5.0",
     "@commitlint/config-conventional": "^19.5.0",