fix: fix BOM parents SQL error and remove unused add children button

Co-authored-by: aider (openai/DeepSeek-V3.2-Thinking) <aider@aider.chat>

inventory-backend/app/api/v1/bom.py

@@ -63,7 +63,7 @@ def get_material_base_list():
 def get_bom_parents():
     """获取所有已定义BOM的父件物料列表"""
     try:
-        subq = db.session.query(distinct(BomTable.parent_id)).subquery()
+        subq = db.session.query(BomTable.parent_id).distinct().subquery()
         parents = MaterialBase.query.join(subq, MaterialBase.id == subq.c.parent_id).all()
         data = [item.to_dict() for item in parents]
         return jsonify({