feat: Add SDK and cURL examples for chunk management, chat assistant, and retrieval (#4310) (#14208)

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)

example/sdk/chunk_example.py

@@ -0,0 +1,92 @@
+#
+#  Copyright 2025 The InfiniFlow Authors. All Rights Reserved.
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+#
+
+"""
+The example demonstrates chunk management (Add, List, Update, Delete, Retrieve)
+within a RAGFlow dataset using the Python SDK.
+"""
+
+from ragflow_sdk import RAGFlow
+import sys
+import time
+import os
+
+HOST_ADDRESS = os.environ.get("RAGFLOW_HOST_ADDRESS", "http://127.0.0.1")
+API_KEY = os.environ.get("RAGFLOW_API_KEY", "ragflow-IzZmY1MGVhYTBhMjExZWZiYTdjMDI0Mm")
+
+try:
+    rag = RAGFlow(api_key=API_KEY, base_url=HOST_ADDRESS)
+
+    # 1. Create a dataset
+    print("Creating dataset...")
+    dataset = rag.create_dataset(name="chunk_example_dataset")
+
+    # 2. Upload a document
+    print("Uploading document...")
+    # Using a simple text content for example
+    content = "RAGFlow is an open-source RAG (Retrieval-Augmented Generation) engine based on deep document understanding."
+    docs = dataset.upload_documents([{"display_name": "sample.txt", "blob": content.encode('utf-8')}])
+    doc = docs[0]
+
+    # 3. Parse the document (required before manual chunk operations if you want it to be processed)
+    print("Parsing document...")
+    dataset.async_parse_documents([doc.id])
+    
+    # Wait for parsing to complete with timeout
+    MAX_WAIT = 120  # seconds
+    elapsed = 0
+    while elapsed < MAX_WAIT:
+        doc_status = dataset.list_documents(id=doc.id)[0]
+        if doc_status.run == "1" and doc_status.progress >= 1.0:
+             print("Parsing completed.")
+             break
+        print(f"Parsing progress: {doc_status.progress:.2f}")
+        time.sleep(2)
+        elapsed += 2
+    else:
+        print("Parsing timed out.")
+        sys.exit(-1)
+
+    # 4. Add a manual chunk
+    print("Adding a manual chunk...")
+    chunk = doc.add_chunk(content="RAGFlow features a streamlined RAG workflow.")
+    print(f"Added chunk ID: {chunk.id}")
+
+    # 5. List chunks
+    print("Listing chunks...")
+    chunks = doc.list_chunks(page=1, page_size=10)
+    print(f"Total chunks found: {len(chunks)}")
+    for i, c in enumerate(chunks):
+        print(f"Chunk {i}: {c.content[:50]}...")
+
+    # 6. Update a chunk
+    print("Updating chunk...")
+    chunk.update({"content": "RAGFlow features a streamlined and powerful RAG workflow."})
+    
+    # 7. Delete the chunk
+    print("Deleting chunk...")
+    doc.delete_chunks([chunk.id])
+
+    # Cleanup
+    print("Cleaning up dataset...")
+    rag.delete_datasets(ids=[dataset.id])
+    
+    print("Chunk example done.")
+    sys.exit(0)
+
+except Exception as e:
+    print(f"An error occurred: {e}")
+    sys.exit(-1)