feat(monospace): add xelatex fontspec header builder

src/main/PdfFontHeader.js

@@ -0,0 +1,29 @@
+'use strict';
+
+const fs = require('fs');
+const os = require('os');
+const path = require('path');
+
+function buildPdfFontHeader(settings, ttfPath, fontFamily) {
+  if (!ttfPath || !fs.existsSync(ttfPath)) {
+    throw new Error(`PdfFontHeader: TTF not found at ${ttfPath}`);
+  }
+  const ligatures = !!(settings && settings.monospaceLigatures === true);
+  const fontDir = path.dirname(ttfPath);
+  const basename = path.basename(ttfPath);
+  const boldName = basename.replace('Regular', 'Bold').replace('Medium', 'Bold');
+  const lines = [
+    `\\setmonofont[Path = ${fontDir}/,`,
+    `             Extension = .ttf,`,
+    `             UprightFont = ${basename},`,
+    `             BoldFont = ${boldName},`,
+    ligatures ? '             Ligatures=TeX,' : '',
+    `             Scale = 0.9]`,
+    `{${fontFamily}}`,
+  ].filter(Boolean);
+  const headerPath = path.join(os.tmpdir(), `monospace-pdf-${Date.now()}-${process.pid}.tex`);
+  fs.writeFileSync(headerPath, lines.join('\n'), 'utf-8');
+  return { headerPath, familyName: fontFamily };
+}
+
+module.exports = { buildPdfFontHeader };