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/http/chat_assistant_example.sh

@@ -0,0 +1,100 @@
+#!/bin/bash
+#
+#  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.
+#
+
+# Variables
+HOST_ADDRESS="${RAGFLOW_HOST_ADDRESS:-http://localhost:9380}"
+API_KEY="${RAGFLOW_API_KEY:-ragflow-IzZmY1MGVhYTBhMjExZWZiYTdjMDI0Mm}"
+
+# Check for jq
+if ! command -v jq &> /dev/null; then
+    echo "jq could not be found, please install it to run this example."
+    exit 1
+fi
+
+# 1. Create a chat assistant
+echo -e "\n-- Create a chat assistant"
+CHAT_RESPONSE=$(curl -s --request POST \
+     --url "${HOST_ADDRESS}/api/v1/chats" \
+     --header 'Content-Type: application/json' \
+     --header "Authorization: Bearer ${API_KEY}" \
+     --data '{
+      "name": "My Assistant",
+      "llm_id": "deepseek-chat"
+      }')
+CHAT_ID=$(echo $CHAT_RESPONSE | jq -r '.data.id')
+echo "Chat Assistant ID: ${CHAT_ID}"
+
+# 2. Create a session for the assistant
+echo -e "\n-- Create a session"
+SESSION_RESPONSE=$(curl -s --request POST \
+     --url "${HOST_ADDRESS}/api/v1/chats/${CHAT_ID}/sessions" \
+     --header 'Content-Type: application/json' \
+     --header "Authorization: Bearer ${API_KEY}" \
+     --data '{
+      "name": "New Session"
+      }')
+SESSION_ID=$(echo $SESSION_RESPONSE | jq -r '.data.id')
+echo "Session ID: ${SESSION_ID}"
+
+# 3. Ask a question (Non-streaming)
+echo -e "\n-- Ask a question (Non-streaming)"
+curl -s --request POST \
+     --url "${HOST_ADDRESS}/api/v1/chats/${CHAT_ID}/completions" \
+     --header 'Content-Type: application/json' \
+     --header "Authorization: Bearer ${API_KEY}" \
+     --data "{
+      \"question\": \"What is RAGFlow?\",
+      \"stream\": false,
+      \"session_id\": \"${SESSION_ID}\"
+      }" | jq .
+
+# 4. Ask a question (Streaming)
+echo -e "\n-- Ask a question (Streaming)"
+# Note: Streaming output will be raw SSE data
+curl -N -s --request POST \
+     --url "${HOST_ADDRESS}/api/v1/chats/${CHAT_ID}/completions" \
+     --header 'Content-Type: application/json' \
+     --header "Authorization: Bearer ${API_KEY}" \
+     --data "{
+      \"question\": \"Tell me more.\",
+      \"stream\": true,
+      \"session_id\": \"${SESSION_ID}\"
+      }"
+
+# 5. List sessions
+echo -e "\n-- List sessions"
+curl -s --request GET \
+     --url "${HOST_ADDRESS}/api/v1/chats/${CHAT_ID}/sessions" \
+     --header "Authorization: Bearer ${API_KEY}" | jq .
+
+# 6. Delete sessions
+echo -e "\n-- Delete sessions"
+curl -s --request DELETE \
+     --url "${HOST_ADDRESS}/api/v1/chats/${CHAT_ID}/sessions" \
+     --header 'Content-Type: application/json' \
+     --header "Authorization: Bearer ${API_KEY}" \
+     --data "{
+      \"ids\": [\"${SESSION_ID}\"]
+      }" | jq .
+
+# Cleanup
+echo -e "\n-- Deleting chat assistant"
+curl -s --request DELETE \
+     --url "${HOST_ADDRESS}/api/v1/chats" \
+     --header 'Content-Type: application/json' \
+     --header "Authorization: Bearer ${API_KEY}" \
+     --data "{\"ids\": [\"${CHAT_ID}\"]}" | jq .