feat(monospace): ExportCss embeds woff2 as base64 in CSS

Self-contained CSS for HTML export and print-preview iframe.

src/main/ExportCss.js

@@ -0,0 +1,34 @@
+'use strict';
+
+const fs = require('fs');
+
+function toDataUri(filePath) {
+  const buf = fs.readFileSync(filePath);
+  return `data:font/woff2;base64,${buf.toString('base64')}`;
+}
+
+function build({ activeFontPath, family, weight = 400, ligatures = false }) {
+  const features = ligatures ? 'normal' : "'liga' 0, 'calt' 0, 'dlig' 0";
+  const faceBlock = activeFontPath
+    ? `@font-face {
+  font-family: '${family}';
+  font-weight: ${weight};
+  font-style: normal;
+  font-display: swap;
+  src: url('${toDataUri(activeFontPath)}') format('woff2');
+}
+`
+    : '';
+
+  return `${faceBlock}code, pre, kbd, samp {
+  font-family: '${family}', monospace;
+  font-feature-settings: ${features};
+}
+pre, code {
+  white-space: pre;
+  tab-size: 4;
+}
+`;
+}
+
+module.exports = { build };

tests/export-css.test.js

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+const fs = require('fs');
+const path = require('path');
+const ExportCss = require('../src/main/ExportCss');
+
+describe('ExportCss.build', () => {
+  const fakeFontPath = path.join(__dirname, 'fixtures', 'fake.woff2');
+  const fixture = Buffer.from('woff2-binary-fake-data');
+
+  beforeAll(() => {
+    fs.mkdirSync(path.dirname(fakeFontPath), { recursive: true });
+    fs.writeFileSync(fakeFontPath, fixture);
+  });
+  afterAll(() => fs.rmSync(path.dirname(fakeFontPath), { recursive: true, force: true }));
+
+  test('emits a self-contained CSS with embedded @font-face', () => {
+    const css = ExportCss.build({ activeFontPath: fakeFontPath, family: 'JetBrains Mono', weight: 400, ligatures: false });
+    expect(css).toMatch(/@font-face\s*\{[^}]*src:\s*url\('data:font\/woff2;base64,/);
+    expect(css).toContain("font-family: 'JetBrains Mono'");
+    expect(css).toMatch(/font-feature-settings:[^;]*liga[^;]*0/);
+  });
+
+  test('falls back to family-only CSS when font path is missing', () => {
+    const css = ExportCss.build({ activeFontPath: null, family: 'Fira Code', weight: 700, ligatures: true });
+    expect(css).not.toContain('data:font/woff2;');
+    expect(css).toContain("font-family: 'Fira Code'");
+  });
+});