Extract hardcoded CDN URLs into a constants file

[coderanik]

Description

Three CDN URLs (for latex.js base.css, article.css, and KaTeX) are hardcoded as strings inside the LatexHtmlPreview component. These should be extracted to a constants file so they can be easily updated when library versions change.

Location

frontend/src/components/LatexHtmlPreview.tsx:62,69,76

Suggested Fix

1. Create frontend/src/lib/cdnUrls.ts:

export const CDN_URLS = {
  LATEX_BASE: "https://cdn.jsdelivr.net/npm/latex.js@0.12.6/dist/css/base.css",
  LATEX_ARTICLE: "https://cdn.jsdelivr.net/npm/latex.js@0.12.6/dist/css/article.css",
  KATEX: "https://cdn.jsdelivr.net/npm/katex@0.16.8/dist/katex.min.css",
};

2. Import and use these constants in LatexHtmlPreview.tsx

Difficulty: Easy

Estimated Time: 20 minutes

[Krshm10]

Hi @coderanik, I'd like to take this issue. I'll work on extracting the hardcoded CDN URLs into a constants file as described. Please assign it to me. Thanks!