DOC-3536: Add minimum TinyMCE version banner to TinyMCE AI Introduction (#4220)

* DOC-3536: Add minimum TinyMCE version banner to TinyMCE AI Introduction

Add an IMPORTANT admonition stating that TinyMCE AI requires TinyMCE 8.4
or later, so readers can confirm version compatibility before adopting
the feature.

* Update modules/ROOT/pages/tinymceai-introduction.adoc

* DOC-3536: Use shared NOTE partial for AI minimum version and add to plugin page

Replace the inline admonition with a reusable partial, change it to a NOTE,
scope the wording to the plugin, and include it on the TinyMCE AI plugin
reference page in addition to the Introduction page.

Author: kemister85

modules/ROOT/pages/tinymceai-introduction.adoc

@@ -9,6 +9,8 @@
 
 Integrate real-time AI writing assistance into your application with TinyMCE AI, with ready-to-go editor features available via the TinyMCE plugin, and custom functionality available via the API -- even outside the editor. Speed up content creation and enhance editorial workflows across a wide range of use cases, from productivity boosts and proof-reading to content quality and consistency. All with your choice of LLM -- including your own.
 
+include::partial$misc/admon-tinymceai-min-version.adoc[]
+
 [[demo]]
 == Demo
 

modules/ROOT/pages/tinymceai.adoc

@@ -14,6 +14,8 @@ include::partial$misc/admon-inline-not-supported.adoc[]
 
 The {pluginname} plugin integrates AI-assisted authoring with rich-text editing. Users can interact through Actions, Reviews, or Conversations that can use relevant context from multiple sources.
 
+include::partial$misc/admon-tinymceai-min-version.adoc[]
+
 [[interactive-example]]
 == Interactive example
 

modules/ROOT/partials/misc/admon-tinymceai-min-version.adoc

@@ -0,0 +1 @@
+NOTE: The {pluginname} plugin requires {productname} 8.4 or later.