feat: Add Markdown to PDF conversion functionality (#59)

* feat: Add Markdown to PDF conversion functionality

- Implement dual-panel interface with live preview
- Support 3 Markdown flavors: GitHub, CommonMark, Pandoc
- Add file upload support for .md files
- Implement image quality settings (High/Medium/Low)
- Add professional user messaging and error handling
- Support all common Markdown elements (headers, lists, tables, code blocks, etc.)
- Add automatic navigation back to tool after completion

Resolves #37

* fix: improve markdown to PDF conversion with math support and better rendering

- Add KaTeX support for mathematical expressions (inline and block math)
- Fix horizontal separator rendering with improved CSS
- Enhance table rendering with proper borders and cell styling
- Replace CDN dependencies with local KaTeX installation
- Add comprehensive math preprocessing for $...$ and 20112...20112 syntax
- Improve markdown preview with real-time math rendering
- Update UI placeholder text with math examples
- Add fallback rendering for math expressions when KaTeX fails

Resolves issues with:
- Horizontal separators not rendering properly
- Tables missing borders and proper structure
- Mathematical expressions not displaying correctly

---------

Co-authored-by: syazkun <mohamadsyazwan193@gmail.com>

src/js/config/tools.ts

@@ -202,7 +202,12 @@ export const categories = [
         icon: 'file-pen',
         subtitle: 'Convert a plain text file into a PDF.',
       },
-      // { id: 'md-to-pdf', name: 'Markdown to PDF', icon: 'file-text', subtitle: 'Convert a Markdown file into a PDF.' },
+      {
+        id: 'md-to-pdf',
+        name: 'Markdown to PDF',
+        icon: 'file-text',
+        subtitle: 'Convert Markdown files to PDF with live preview.',
+      },
       // { id: 'scan-to-pdf', name: 'Scan to PDF', icon: 'camera', subtitle: 'Use your camera to create a scanned PDF.' },
       {
         id: 'word-to-pdf',