ModelTranslator: extend seam angle sweep to 15deg for QR smooth meshes

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Tools/ModelTranslator/tests/test_bl_decimate.py

@@ -151,5 +151,18 @@ class TestPickBestCandidate(unittest.TestCase):
         self.assertEqual(best["angle"], 55)
 
 
+class TestSeamAngleSweep(unittest.TestCase):
+    def test_descending(self):
+        s = list(bd.SEAM_ANGLE_SWEEP)
+        self.assertEqual(s, sorted(s, reverse=True))
+
+    def test_reaches_low_angle(self):
+        # 需下探到 <=30° 以覆盖 QR 光滑四边网格（实测 guang 30° 才过门）
+        self.assertLessEqual(min(bd.SEAM_ANGLE_SWEEP), 30.0)
+
+    def test_below_first_angle(self):
+        self.assertLess(max(bd.SEAM_ANGLE_SWEEP), bd.SEAM_ANGLE_DEG)
+
+
 if __name__ == "__main__":
     unittest.main()