Clarify audience of root vs package AGENTS.md

The root AGENTS.md (symlinked as CLAUDE.md) is for contributors working
on the project. Add a pointer to python/datafusion/AGENTS.md which is
the user-facing DataFrame API guide shipped with the package. Also add
the Apache license header to the package AGENTS.md.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: timsaucer

AGENTS.md

@@ -17,7 +17,14 @@
   under the License.
 -->
 
-# Agent Instructions
+# Agent Instructions for Contributors
+
+This file is for agents working **on** the datafusion-python project (developing,
+testing, reviewing). If you need to **use** the DataFusion DataFrame API (write
+queries, build expressions, understand available functions), see the user-facing
+guide at [`python/datafusion/AGENTS.md`](python/datafusion/AGENTS.md).
+
+## Skills
 
 This project uses AI agent skills stored in `.ai/skills/`. Each skill is a directory containing a `SKILL.md` file with instructions for performing a specific task.
 

python/datafusion/AGENTS.md

@@ -1,3 +1,22 @@
+<!---
+  Licensed to the Apache Software Foundation (ASF) under one
+  or more contributor license agreements.  See the NOTICE file
+  distributed with this work for additional information
+  regarding copyright ownership.  The ASF licenses this file
+  to you 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.
+-->
+
 # DataFusion Python DataFrame API Guide
 
 ## What Is DataFusion?