feat(export): themable PDF/Word exports; Windows CI green (v4.7.1)

Export themes:
- Six presets in the export dialog (basic + advanced modes) for PDF/DOCX:
  Default, Modern, Classic, Sepia, Minimal, Elegant
- PDF: LaTeX header (xcolor/titlesec) recolors headings, adds section
  rules and colored links — core-TeX packages only, hex-literal only
  (no injection surface)
- DOCX: styles.xml surgery recolors Heading1-6/Title/Subtitle/Hyperlink
  and swaps heading/body fonts; verified end-to-end against a real
  pandoc-produced docx
- Themes ride along in export presets (unknown ids fall back to Default)

Windows CI fixes:
- pdfjs standardFontDataUrl now a file:// URL (backslash paths failed
  pdfjs's trailing-slash validation, breaking extractText/extractImages)
- sharp temp cleanup EPERM retries; path-separator assertions; pdfjs
  test timeouts raised; batch suite testTimeout 30s

648/648 tests green; 4.7.1 linux+win artifacts rebuilt.

tests/monospace-font-config.test.js

@@ -22,7 +22,10 @@ describe('MonospaceFontConfig', () => {
       (p) => !p.includes('app.asar.unpacked') && p.endsWith('JetBrainsMono-Regular.ttf')
     );
     const p = MonospaceFontConfig.getMonoFontTtfPath('jetbrains-mono', 400);
-    expect(p).toMatch(/assets\/fonts\/JetBrainsMono-Regular\.ttf$/);
+    // Normalize separators: Windows paths are backslash-joined
+    expect(p.split(require('path').sep).join('/')).toMatch(
+      /assets\/fonts\/JetBrainsMono-Regular\.ttf$/
+    );
   });
 
   test('returns packaged asar.unpacked path when present and file exists', () => {