Closes#4310
### What problem does this PR solve?
Issue #4310 requests practical examples for the RAGFlow SDK and HTTP API
to help developers get started faster. The existing `example/sdk/`
folder only contains `dataset_example.py`. This PR fills the remaining
gaps by adding examples for three key API areas not yet covered in
`main` or by other open PRs (#13904, #13284):
- **Chunk management** — add, list, update, delete, and retrieve chunks
within a dataset
- **Chat assistant** — create a chat assistant, open a session, send
messages (streaming and non-streaming), and clean up
- **Retrieval** — perform semantic retrieval across one or multiple
datasets
### Type of change
- [x] Documentation Update
- [x] New Feature (non-breaking change which adds functionality)
### What problem does this PR solve?
Support getting aggregated parsing status to dataset via the API
Issue: #12810
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
Co-authored-by: heyang.why <heyang.why@alibaba-inc.com>
### What problem does this PR solve?
- typos
- IDE warnings
### Type of change
- [x] Refactoring
---------
Signed-off-by: Jin Hai <haijin.chn@gmail.com>
### What problem does this PR solve?
### Type of change
- [x] Refactoring
- [x] Performance Improvement
Signed-off-by: zhanluxianshen <zhanluxianshen@163.com>
### What problem does this PR solve?
Add test for document
### Type of change
- [x] New Feature (non-breaking change which adds functionality)
Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>
### What problem does this PR solve?
Fix bugs in api.
Add simple examples for api.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
- [x] New Feature (non-breaking change which adds functionality)
---------
Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>
Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>
