ModelTranslator: uvgate 回退标注改前缀匹配——兼容 +uvpm 后缀

- 新增 seam_fallback_label 纯函数：前缀匹配转换 seam* → seam_fallback*，保留后缀
- main() 调用改为函数式，避免等值判断失效
- 测试覆盖：plain seam、seam+uvpm、smart_fallback 透传

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

Tools/ModelTranslator/bl_uvgate.py

@@ -7,6 +7,13 @@ import sys
 sys.path.insert(0, os.path.dirname(os.path.abspath(__file__)))
 
 
+def seam_fallback_label(mode):
+    """回退产物标注：seam 系模式改 seam_fallback（保留 +uvpm 等后缀）。"""
+    if mode.startswith("seam"):
+        return "seam_fallback" + mode[len("seam"):]
+    return mode
+
+
 def main():
     import bpy
     import json
@@ -42,8 +49,7 @@ def main():
         warnings.append("%s 输出无 UV，回退 seam" % mode_label)
 
     m = _do_unwrap(obj, "seam", warnings)   # 内部自带 smart 回退
-    if m["mode"] == "seam":
-        m["mode"] = "seam_fallback"
+    m["mode"] = seam_fallback_label(m["mode"])
     bpy.ops.object.select_all(action='DESELECT')
     obj.select_set(True)
     bpy.ops.export_scene.fbx(filepath=os.path.abspath(fbx), use_selection=True,