docs: publish SKILL.md on the docs site via myst include

Adds a new `skill` page that embeds the repo-root `SKILL.md` through the
myst `{include}` directive, so the agent-facing guide lives on the
published docs site without duplication. The page is wired into the
User Guide toctree. Implements PR 4a of the plan in #1394.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: timsaucer

docs/source/index.rst

@@ -78,6 +78,7 @@ Example
    user-guide/configuration
    user-guide/sql
    user-guide/upgrade-guides
+   skill
 
 
 .. _toc.contributor_guide:

docs/source/skill.md

@@ -0,0 +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.
+-->
+
+```{include} ../../SKILL.md
+:start-line: 4
+```