### Summary
As title
This PR fixes dataset index task creation failing with unsupported data
type: entity.JSONMap when loading document chunking config.
#### issues:
```
2026/06/30 15:19:40 /home/infiniflow/Documents/development/ragflow/internal/dao/document.go:162
[error] unsupported data type: ragflow/internal/entity.JSONMap
```
#### Changes:
+ Adds the missing GORM type:longtext tag to ParserConfig in
DocumentDAO.GetChunkingConfig.
+ Adds a DAO regression test covering GetChunkingConfig joins across
document, knowledgebase, and tenant while scanning parser_config.