Improve the admin panel extension page (#3003)

* Rework the page to add information about building a plugin

* Remove links to plugin development guides

* Add short decision table

* Move HotReloading snippet

* Convert link to Strapi Marketplace to an external link

Author: pwizla

docusaurus/docs/cms/admin-panel-customization/extension.md

@@ -2,13 +2,10 @@
 title: Admin panel extension
 description: Learn more about extending Strapi's admin panel.
 displayed_sidebar: cmsSidebar
-toc_max_heading_level: 4
 tags:
 - admin panel 
 - admin panel customization
-
 ---
-
 import HotReloading from '/docs/snippets/hot-reloading-admin-panel.md'
 
 # Admin panel extension
@@ -19,17 +16,31 @@ Extending Strapi's admin panel means leveraging its React foundation to adapt an
 
 There are 2 use cases where you might want to extend the admin panel:
 
-- As a Strapi plugin developer, you want to develop a Strapi plugin that extends the admin panel **everytime it's installed in any Strapi application**.
+| Approach | Scope | Entry point | Docs |
+|---|---|---|---|
+| Local extension | One Strapi project | `/src/admin/app.(js\|ts)` and `/src/admin/extensions/` | [Admin panel customization](/cms/admin-panel-customization) |
+| Plugin extension | Any project that installs your plugin | `[plugin-name]/admin/src/index.(js\|ts)` | [Admin Panel API overview](/cms/plugins-development/admin-panel-api) |
 
-  👉 This can be done by taking advantage of the [Admin Panel API for plugins](/cms/plugins-development/admin-panel-api).
+- As a Strapi plugin developer, you want to develop a Strapi plugin that extends the admin panel **everytime it's installed in any Strapi application**.
+  👉 This can be done by taking advantage of the [Admin Panel API for plugins](/cms/plugins-development/admin-panel-api), which lets you add navigation links and settings sections, inject React components into predefined areas, manage state with Redux, extend the Content Manager's Edit and List views, and more.
 
 - As a Strapi developer, you want to develop a unique solution for a Strapi user who only needs to extend a specific instance of a Strapi application.
-
   👉 This can be done by directly updating the `/src/admin/app` file, which can import any file located in `/src/admin/extensions`.
 
+<HotReloading />
+
+## When to consider a plugin instead
+
+Starting with a direct customization in `/src/admin/app` is the right default for project-specific needs. Consider moving to a plugin-based approach when one or more of these signals appear:
+
+- You are duplicating the same admin customization across several Strapi projects.
+- You want to version and distribute the extension — either internally or through the <ExternalLink text="Strapi Marketplace" to="https://market.strapi.io/"/>.
+- You need stronger automated testing independent from a single project codebase.
+- Multiple teams need shared ownership and release management for the same extension.
+
+For a full introduction to plugin development, see [Developing Strapi plugins](/cms/plugins-development/developing-plugins).
+
 :::strapi Additional resources
-* If you're searching for ways of replacing the default Rich text editor, please refer to the [corresponding page](/cms/admin-panel-customization/wysiwyg-editor).
-* The <ExternalLink to="https://design-system.strapi.io/?path=/docs/getting-started-welcome--docs" text="Strapi Design System documentation"/> also provide extensive additional information on developing for Strapi's admin panel.
+* If you're looking for ways of replacing the default Rich text editor, refer to the [corresponding page](/cms/admin-panel-customization/wysiwyg-editor).
+* To understand how plugins integrate with the Strapi admin panel, start with the [Admin Panel API overview](/cms/plugins-development/admin-panel-api).
 :::
-
-<HotReloading />