feat: add DXF (R12) and SVG exporters

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

src/lib/export-dxf.ts

@@ -0,0 +1,24 @@
+import { formatMm, shapeSize } from './geometry';
+import type { Shape } from './types';
+
+/** Minimal ASCII DXF R12: one closed POLYLINE per ring, units mm, Y axis up. */
+export function toDxf(shapeMm: Shape): string {
+  const { height } = shapeSize(shapeMm);
+  const out: (string | number)[] = [
+    0, 'SECTION', 2, 'HEADER',
+    9, '$ACADVER', 1, 'AC1009',
+    9, '$INSUNITS', 70, 4,
+    0, 'ENDSEC',
+    0, 'SECTION', 2, 'ENTITIES',
+  ];
+  for (const ring of [shapeMm.outer, ...shapeMm.holes]) {
+    out.push(0, 'POLYLINE', 8, '0', 66, 1, 70, 1, 10, '0.0', 20, '0.0', 30, '0.0');
+    for (const p of ring) {
+      out.push(0, 'VERTEX', 8, '0', 10, formatMm(p.x), 20, formatMm(height - p.y), 30, '0.0');
+    }
+    out.push(0, 'SEQEND', 8, '0');
+  }
+  out.push(0, 'ENDSEC', 0, 'EOF');
+  // RDWorks is a Windows tool; CRLF is the most widely accepted DXF line ending.
+  return out.join('\r\n') + '\r\n';
+}

src/lib/export-svg.ts

@@ -0,0 +1,20 @@
+import { formatMm, shapeSize } from './geometry';
+import type { Point, Shape } from './types';
+
+export function toSvg(shapeMm: Shape): string {
+  const { width, height } = shapeSize(shapeMm);
+  const w = formatMm(width);
+  const h = formatMm(height);
+  const d = [shapeMm.outer, ...shapeMm.holes].map(ringPath).join(' ');
+  return [
+    '<?xml version="1.0" encoding="UTF-8"?>',
+    `<svg xmlns="http://www.w3.org/2000/svg" width="${w}mm" height="${h}mm" viewBox="0 0 ${w} ${h}">`,
+    `  <path d="${d}" fill="none" fill-rule="evenodd" stroke="#ff0000" stroke-width="0.1"/>`,
+    '</svg>',
+    '',
+  ].join('\n');
+}
+
+function ringPath(ring: Point[]): string {
+  return 'M' + ring.map((p) => `${formatMm(p.x)},${formatMm(p.y)}`).join(' L') + ' Z';
+}