[fix] doc: drop the contents:: directive, name the plugin consistently

Furo renders its own page-local table of contents and reports an error
when a page adds one with contents::.  No other page in the tree uses
that directive; these two now follow suit.

The plugin is named "AI Summary" where the name of the plugin is meant,
and "AI summary" where the generated text itself is meant.  That also
fixes the entry in the plugin navigation, which takes its label from the
page title.

Two references to the configuration page rendered as its title, the bare
YAML key "ai_summary:", which reads as a typo in a sentence.  They now
carry explicit link text.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/dev/plugins/ai_summary.rst

@@ -1,23 +1,18 @@
 .. _ai_summary plugin:
 
 ==========
-AI summary
+AI Summary
 ==========
 
 .. sidebar:: Further reading ..
 
-   - :ref:`settings ai_summary`
+   - :ref:`Configuration <settings ai_summary>`
    - :ref:`dev plugin`
    - :ref:`result types`
 
-.. contents::
-   :depth: 2
-   :local:
-   :backlinks: entry
-
-The AI summary plugin shows a generated answer above the search results.  The
-text comes from an LLM server the administrator runs; see :ref:`settings
-ai_summary` for how to set one up.
+The AI Summary plugin shows a generated answer above the search results.  The
+text comes from an LLM server the administrator runs; see :ref:`its
+configuration <settings ai_summary>` for how to set one up.
 
 The interesting part of this plugin is *when* things happen.  Generating an
 answer takes seconds, and a search engine that waits seconds before painting