feat(curd): 关联表优化支持 add relation support and optimize model associations

- Add support for handling relations in CURD operations
- Optimize model associations to use hasOne instead of belongsTo
- Implement field selection for relations
- Update controller to handle AJAX requests and return JSON data Modify model to include relation methods

app/admin/service/curd/templates/model/relation.code

@@ -1,5 +1,5 @@
 
     public function {{relationMethod}}()
     {
-        return $this->belongsTo('{{relationModel}}', '{{foreignKey}}', '{{primaryKey}}');
+        return $this->hasOne({{relationModel}}, '{{foreignKey}}', '{{primaryKey}}'){{relationFields}};
     }