ModelTranslator: UV 质量门拆分并校准——翻转 2% / 重叠 8%（well1500 seam 不再误回退）

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

Tools/ModelTranslator/bl_decimate.py

@@ -24,7 +24,8 @@ def within_tolerance(target, actual, tol=TOLERANCE):
     return abs(actual - target) <= target * tol
 
 
-UV_BAD_TOL = 0.02   # 质量门：UV 翻转/重叠面占比超此值则回退 smart_project
+UV_FLIP_TOL = 0.02      # 质量门：UV 翻转面占比超此值回退 smart_project
+UV_OVERLAP_TOL = 0.08   # 质量门：UV 重叠面占比阈值（手工 UV 同口径约 5%，灾难性失败 >20%）
 
 
 def count_islands(n_faces, adjacent_pairs):
@@ -199,7 +200,7 @@ def _do_unwrap(obj, mode, warnings):
         _unwrap_seam(obj, warnings)
         m = _collect_uv_metrics(obj)
         overlap = m["overlap"] or 0.0
-        if m["flipped"] <= UV_BAD_TOL and overlap <= UV_BAD_TOL:
+        if m["flipped"] <= UV_FLIP_TOL and overlap <= UV_OVERLAP_TOL:
             m["mode"] = "seam"
             return m
         warnings.append("seam 展开质量不达标（翻转 %.1f%% 重叠 %s），回退 smart_project"