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/retrieval_example.sh

@@ -0,0 +1,72 @@
+#!/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
+
+# 0. Setup: Create a dataset to retrieve from
+echo -e "\n-- Creating a dataset"
+DATASET_ID=$(curl -s --request POST \
+     --url "${HOST_ADDRESS}/api/v1/datasets" \
+     --header 'Content-Type: application/json' \
+     --header "Authorization: Bearer ${API_KEY}" \
+     --data '{"name": "retrieval_shell_example"}' | jq -r '.data.id')
+echo "Dataset ID: ${DATASET_ID}"
+
+# 1. Perform semantic retrieval from a dataset
+echo -e "\n-- Perform semantic retrieval"
+curl -s --request POST \
+     --url "${HOST_ADDRESS}/api/v1/retrieval" \
+     --header 'Content-Type: application/json' \
+     --header "Authorization: Bearer ${API_KEY}" \
+     --data "{
+      \"dataset_ids\": [\"${DATASET_ID}\"],
+      \"question\": \"What is RAGFlow?\",
+      \"page\": 1,
+      \"page_size\": 5,
+      \"similarity_threshold\": 0.2,
+      \"vector_similarity_weight\": 0.3,
+      \"top_k\": 1024
+      }" | jq .
+
+# 2. Perform retrieval with keyword search enabled
+echo -e "\n-- Perform retrieval with keyword search"
+curl -s --request POST \
+     --url "${HOST_ADDRESS}/api/v1/retrieval" \
+     --header 'Content-Type: application/json' \
+     --header "Authorization: Bearer ${API_KEY}" \
+     --data "{
+      \"dataset_ids\": [\"${DATASET_ID}\"],
+      \"question\": \"workflow features\",
+      \"keyword\": true,
+      \"top_k\": 10
+      }" | jq .
+
+# Cleanup
+echo -e "\n-- Cleaning up dataset"
+curl -s --request DELETE \
+     --url "${HOST_ADDRESS}/api/v1/datasets" \
+     --header 'Content-Type: application/json' \
+     --header "Authorization: Bearer ${API_KEY}" \
+     --data "{\"ids\": [\"${DATASET_ID}\"]}" | jq .