feat(cadfs): 补齐核心建模能力并建立代表性回归

- 新增 loft、双向切除、through-all/up-to-next 等 CADFS lowering 与 engine 支持
- 支持多种 reference plane、B-spline profile 和 circular pattern replay
- 保留 transform 历史，并烘焙安全的单源平移/旋转变换
- 改进 selector 绑定、拓扑快照和 pattern 变换处理
- 建立 17 个代表样本的转换、重建与比较回归工具链
- 补充 schema、author guidance、运行时和几何回归测试

backend/tests/test_author_guidance.py

@@ -73,7 +73,7 @@ class AuthorGuidanceTests(unittest.TestCase):
             self.assertLessEqual(len(selection.content), 1_200)
             self.assertIn("世界坐标", selection.content)
             covered.update(section_id for section_id in selection.section_ids if section_id.startswith("op-"))
-        self.assertEqual(covered, {"op-extrude-add", "op-extrude-cut", "op-revolve", "op-hole", "op-reference", "op-pattern", "op-finish", "op-sphere"})
+        self.assertEqual(covered, {"op-extrude-add", "op-extrude-cut", "op-loft", "op-revolve", "op-hole", "op-reference", "op-pattern", "op-finish", "op-sphere", "op-primitives", "op-thread"})
 
     def test_phase_repair_and_budget_selection_are_stable(self) -> None:
         guidance = FileAuthorGuidance(GUIDANCE_ROOT, max_chars=3_600)