fix: drop glare holes before the margin and never auto-pick specks

Filtering holes after the margin let -2 mm grow 1 mm specks past the
3 mm cutoff, and could drop real holes shrunk by a positive margin.

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

tests/fixtures.test.ts

@@ -34,7 +34,7 @@ describe.skipIf(cases.length === 0)('detect on real photos', () => {
   it.each(cases)('$file', (c) => {
     const image = readJpeg(dir + c.file);
     const threshold = c.threshold ?? otsuThreshold(cv, image);
-    const shape = detect(cv, image, { threshold, invert: c.invert, seed: c.seed, marginPx: 0 });
+    const shape = detect(cv, image, { threshold, invert: c.invert, seed: c.seed, marginPx: 0, minHolePx: 3 * c.pxPerMm });
     expect(shape).not.toBeNull();
     const mm = prepareForExport(shape!, c.pxPerMm)!;
     const size = shapeSize(mm);