server: (UI) add syntax highlighting and latex math rendering (#10808)

* add code highlighting and math formatting

* code cleanup

* build public/index.html

* rebuild public/index.html

* fixed coding style

* fixed coding style

* style fixes

* highlight: smaller bundle size, fix light & dark theme

* remove katex

* add bundle size check

* add more languages

* add php

* reuse some langs

* use gzip

* Revert "remove katex"

This reverts commit c0e5046acc.

* use better maintained @vscode/markdown-it-katex

* fix gzip non deterministic

* ability to add a demo conversation for dev

* fix latex rendering

* add comment

* latex codeblock as code

---------

Co-authored-by: Xuan Son Nguyen <son@huggingface.co>

examples/server/webui/src/katex-gpt.js

@@ -0,0 +1,66 @@
+import katex from 'katex';
+
+// Adapted from https://github.com/SchneeHertz/markdown-it-katex-gpt
+// MIT license
+
+const defaultOptions = {
+  delimiters: [
+    { left: '\\[', right: '\\]', display: true },
+    { left: '\\(', right: '\\)', display: false },
+  ],
+};
+
+export function renderLatexHTML(content, display = false) {
+  return katex.renderToString(content, {
+    throwOnError: false,
+    output: 'mathml',
+    displayMode: display,
+  });
+}
+
+function escapedBracketRule(options) {
+  return (state, silent) => {
+    const max = state.posMax;
+    const start = state.pos;
+
+    for (const { left, right, display } of options.delimiters) {
+
+      // Check if it starts with the left delimiter
+      if (!state.src.slice(start).startsWith(left)) continue;
+
+      // Skip the length of the left delimiter
+      let pos = start + left.length;
+
+      // Find the matching right delimiter
+      while (pos < max) {
+        if (state.src.slice(pos).startsWith(right)) {
+          break;
+        }
+        pos++;
+      }
+
+      // No matching right delimiter found, skip to the next match
+      if (pos >= max) continue;
+
+      // If not in silent mode, convert LaTeX formula to MathML
+      if (!silent) {
+        const content = state.src.slice(start + left.length, pos);
+        try {
+          const renderedContent = renderLatexHTML(content, display);
+          const token = state.push('html_inline', '', 0);
+          token.content = renderedContent;
+        } catch (e) {
+          console.error(e);
+        }
+      }
+
+      // Update position, skip the length of the right delimiter
+      state.pos = pos + right.length;
+      return true;
+    }
+  }
+}
+
+export default function (md, options = defaultOptions) {
+  md.inline.ruler.after('text', 'escaped_bracket', escapedBracketRule(options));
+}