[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>

searx/plugins/ai_summary.py

@@ -1,5 +1,5 @@
 # SPDX-License-Identifier: AGPL-3.0-or-later
-"""Implementation of the AI summary plugin, which shows a generated answer above
+"""Implementation of the AI Summary plugin, which shows a generated answer above
 the search results.  The answer comes from an LLM server that implements the
 `OpenAI chat completions API`_ (Ollama, vLLM, llama.cpp, LM Studio, Hugging Face
 TGI, ...) and that the administrator runs.
@@ -135,7 +135,7 @@ class SXNGPlugin(Plugin):
 
         self.info = PluginInfo(
             id=self.id,
-            name=gettext("AI summary"),
+            name=gettext("AI Summary"),
             description=gettext(
                 "Show an AI generated summary of the search query on top of the"
                 " result page (uses a local LLM server, see the settings below)."