feat(math): add optional MathJax support (#707)

* feat: add MathJax option

* docs: move math engine note

* refactor: update LaTeX documentation and improve MathJax integration

- Adjusted LaTeX documentation for clarity and formatting.
- Enhanced MathJax configuration in the templates to support both KaTeX and MathJax rendering.
- Removed deprecated comments and streamlined the script loading process for MathJax.
- Updated the passthrough extension settings in the Hugo configuration for better compatibility with LaTeX math expressions.

* docs: simplify LaTeX documentation and clarify configuration steps

- Updated LaTeX documentation to reflect that KaTeX is enabled by default, removing the need for manual activation.
- Added examples for using LaTeX math expressions and clarified the configuration for the passthrough extension in Hugo.
- Enhanced MathJax section to emphasize its use as an alternative rendering engine.

layouts/_partials/scripts/mathjax.html

@@ -0,0 +1,21 @@
+{{/* MathJax */}}
+{{ $mathjaxVersion := site.Params.math.mathjaxVersion | default "3" -}}
+{{ $mathjaxJsUrl := printf "https://cdn.jsdelivr.net/npm/mathjax@%s/es5/tex-chtml.js" $mathjaxVersion -}}
+<script defer id="MathJax-script" src="{{ $mathjaxJsUrl }}" crossorigin="anonymous" async></script>
+<script>
+  MathJax = {
+    loader: {
+      load: ["ui/safe"],
+    },
+    tex: {
+      displayMath: [
+        ["\\[", "\\]"],
+        ["$$", "$$"],
+      ],
+      inlineMath: [
+        ["\\(", "\\)"],
+        ["$", "$"],
+      ],
+    },
+  };
+</script>