feat: 更新分期方案初始化脚本，匹配最新表结构

- 更新表名和字段名为小写格式
- 修正字段类型以匹配实体类定义
- 新增缺失字段：scheme_type, down_payment_ratio等
- 添加索引优化查询性能
- 完善表和字段注释

LCXiaoguan-ui/LICENSE

@@ -0,0 +1,20 @@
+The MIT License (MIT)
+
+Copyright (c) 2019 RuoYi-Vue-Plus
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
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+the Software, and to permit persons to whom the Software is furnished to do so,
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+The above copyright notice and this permission notice shall be included in all
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