add missing mathjax.js

docs/javascripts/mathjax.js

@@ -0,0 +1,27 @@
+// MathJax configuration for pymdownx.arithmatex (generic mode).
+// Must load BEFORE the MathJax library (see extra_javascript in zensical.toml).
+window.MathJax = {
+  tex: {
+    inlineMath: [["\\(", "\\)"]],
+    displayMath: [["\\[", "\\]"]],
+    processEscapes: true,
+    processEnvironments: true,
+  },
+  options: {
+    ignoreHtmlClass: ".*|",
+    processHtmlClass: "arithmatex",
+  },
+};
+
+// With navigation.instant, pages are swapped in without a full reload, so
+// MathJax's startup typeset never sees the new content. Re-typeset on every
+// page change emitted by the theme's document$ observable.
+if (window.document$ && typeof window.document$.subscribe === "function") {
+  window.document$.subscribe(() => {
+    if (!window.MathJax || !MathJax.startup || !MathJax.typesetPromise) return;
+    MathJax.startup.output.clearCache();
+    MathJax.typesetClear();
+    MathJax.texReset();
+    MathJax.typesetPromise();
+  });
+}