docs: bifurcate documentation into user, admin, and developer sections

Major restructuring of documentation to separate concerns:

**New Structure:**
- `/docs/` - User-facing docs (intro, quickstart, databases, using-superset, faq)
- `/admin-docs/` - Administrator docs (installation, configuration, security)
- `/developer-docs/` - Developer docs (contributing, extensions, guidelines, testing)

**Changes:**
- Move installation, configuration, and security docs to admin_docs/
- Move contributing, extensions, guidelines, and testing to developer_docs/
- Rename developer_portal to developer_docs (with underscore to hyphen in URL)
- Add sidebarAdminDocs.js for admin documentation navigation
- Update versions-config.json with new doc sections
- Update docusaurus.config.ts with new plugins and redirects
- Update internal links in versioned docs (6.0.0) to use new paths
- Keep user-facing content (databases, using-superset, faq) in main docs

This separation makes it clearer which documentation is relevant for:
- End users exploring and visualizing data
- Administrators deploying and configuring Superset
- Developers contributing to or extending Superset

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/developer_docs/components/ui/collapse.mdx

@@ -0,0 +1,106 @@
+---
+title: Collapse
+sidebar_label: Collapse
+---
+
+<!--
+    Licensed to the Apache Software Foundation (ASF) under one
+    or more contributor license agreements.  See the NOTICE file
+    distributed with this work for additional information
+    regarding copyright ownership.  The ASF licenses this file
+    to you under the Apache License, Version 2.0 (the
+    "License"); you may not use this file except in compliance
+    with the License.  You may obtain a copy of the License at
+
+      http://www.apache.org/licenses/LICENSE-2.0
+
+    Unless required by applicable law or agreed to in writing,
+    software distributed under the License is distributed on an
+    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+    KIND, either express or implied.  See the License for the
+    specific language governing permissions and limitations
+    under the License.
+-->
+
+import { StoryWithControls } from '../../../src/components/StorybookWrapper';
+
+# Collapse
+
+The Collapse component from Superset's UI library.
+
+## Live Example
+
+<StoryWithControls
+  component="Collapse"
+  props={{
+  ghost: false,
+  bordered: true,
+  accordion: false,
+  animateArrows: false,
+  modalMode: false
+}}
+  controls={[
+  {
+    name: "ghost",
+    label: "Ghost",
+    type: "boolean"
+  },
+  {
+    name: "bordered",
+    label: "Bordered",
+    type: "boolean"
+  },
+  {
+    name: "accordion",
+    label: "Accordion",
+    type: "boolean"
+  },
+  {
+    name: "animateArrows",
+    label: "Animate Arrows",
+    type: "boolean"
+  },
+  {
+    name: "modalMode",
+    label: "Modal Mode",
+    type: "boolean"
+  }
+]}
+/>
+
+## Try It
+
+Edit the code below to experiment with the component:
+
+```tsx live
+function Demo() {
+  return (
+    <Collapse
+      bordered
+    />
+  );
+}
+```
+
+## Props
+
+| Prop | Type | Default | Description |
+|------|------|---------|-------------|
+| `ghost` | `boolean` | `false` | - |
+| `bordered` | `boolean` | `true` | - |
+| `accordion` | `boolean` | `false` | - |
+| `animateArrows` | `boolean` | `false` | - |
+| `modalMode` | `boolean` | `false` | - |
+
+## Import
+
+```tsx
+import { Collapse } from '@superset/components';
+```
+
+---
+
+:::tip[Improve this page]
+This documentation is auto-generated from the component's Storybook story.
+Help improve it by [editing the story file](https://github.com/apache/superset/edit/master/superset-frontend/packages/superset-ui-core/src/components/Collapse/Collapse.stories.tsx).
+:::