fix(markup): raise KaTeX MAX_CHARS limit to 10000 (#39387) (#39389)

Backport #39387 by @Copilot

Fix #39386

web_src/js/markup/math.ts

@@ -20,7 +20,7 @@ export async function initMarkupCodeMath(elMarkup: HTMLElement): Promise<void> {
       import('katex/dist/katex.css'),
     ]);
 
-    const MAX_CHARS = 1000;
+    const MAX_CHARS = 10000;
     const MAX_SIZE = 25;
     const MAX_EXPAND = 1000;