[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/admin/settings/settings_ai_summary.rst

@@ -10,7 +10,7 @@
    - :ref:`settings plugins`
    - :ref:`settings preferences`
 
-Configuration of the :ref:`AI summary plugin <ai_summary plugin>`, which shows a
+Configuration of the :ref:`AI Summary plugin <ai_summary plugin>`, which shows a
 short AI generated answer above the search results.
 
 The text is produced by an **LLM server that you run** -- SearXNG does not ship
@@ -18,11 +18,6 @@ a model and does not talk to any AI provider on its own.  Anything that speaks
 the `OpenAI chat completions API`_ works: `Ollama`_, vLLM, llama.cpp, LM Studio,
 Hugging Face TGI and others.  The plugin is not activated by default.
 
-.. contents::
-   :depth: 2
-   :local:
-   :backlinks: entry
-
 
 .. _ai_summary quickstart:
 
@@ -76,7 +71,7 @@ Add this to your ``settings.yml``:
 .. warning::
 
    A ``plugins:`` block **replaces** the default list, it is not merged into it
-   (:ref:`settings plugins`).  If you list only the AI summary plugin, every
+   (:ref:`settings plugins`).  If you list only the AI Summary plugin, every
    other plugin is switched off.  That is why the block above repeats the
    defaults -- drop the lines for plugins you do not want.