feat: add DXF (R12) and SVG exporters

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/export-svg.test.ts

@@ -0,0 +1,27 @@
+import { describe, expect, it } from 'vitest';
+import { toSvg } from '../src/lib/export-svg';
+
+const shape = {
+  outer: [{ x: 0, y: 0 }, { x: 100, y: 0 }, { x: 100, y: 50 }, { x: 0, y: 50 }],
+  holes: [[{ x: 10, y: 10 }, { x: 20, y: 10 }, { x: 20, y: 20.5 }]],
+};
+
+describe('toSvg', () => {
+  it('declares its size in mm with a matching viewBox', () => {
+    const svg = toSvg(shape);
+    expect(svg).toContain('width="100mm"');
+    expect(svg).toContain('height="50mm"');
+    expect(svg).toContain('viewBox="0 0 100 50"');
+  });
+
+  it('writes one closed subpath per ring in a single evenodd path', () => {
+    const svg = toSvg(shape);
+    const d = svg.match(/ d="([^"]+)"/)![1];
+    expect(d.match(/M/g)).toHaveLength(2);
+    expect(d.match(/Z/g)).toHaveLength(2);
+    expect(d).toContain('M0,0 L100,0 L100,50 L0,50 Z');
+    expect(d).toContain('20,20.5');
+    expect(svg).toContain('fill-rule="evenodd"');
+    expect(svg).toContain('fill="none"');
+  });
+});