docs: cut 6.1.0 versions for docs, admin_docs, developer_docs, components

Snapshots all four versioned Docusaurus sections at v6.1.0, cut from
master after the version-cutting tooling (#39837) and broken-internal-
links fixes (#40102) landed. Captures fresh auto-generated content and
freezes data dependencies so the historical snapshot stays correct.

Versioning behavior: lastVersion stays at current for every section,
so the canonical URLs (/docs/..., /admin-docs/..., /developer-docs/...,
/components/...) continue to render content from master. The current
version is consistently labeled "Next" with an unreleased banner, and
6.1.0 is a historical pin accessible only via its explicit version
segment.

Component playground: previously disabled: true in versions-config.json,
now enabled and versioned. The plugin block in docusaurus.config.ts
was already gated only by the disabled flag, so no other code changes
were needed to bring it back online.

Snapshot includes:
- All MDX content for the four sections.
- Auto-gen captured fresh: 74 database pages (engine spec metadata),
  ~1,800 API reference files (openapi.json), 59 component pages
  (Storybook stories).
- Data imports frozen at cut time into snapshot-local _versioned_data/
  dirs:
    versioned_docs/version-6.1.0/_versioned_data/src/data/databases.json
      (canonical 80-database diagnostics from master, preserved by the
      generator's input-hash cache)
    admin_docs_versioned_docs/version-6.1.0/_versioned_data/data/countries.json
    admin_docs_versioned_docs/version-6.1.0/_versioned_data/static/feature-flags.json
    developer_docs_versioned_docs/version-6.1.0/_versioned_data/static/data/components.json
- Import paths in deeply-nested files rewritten so they still resolve
  from one directory deeper inside the snapshot.

Verified via full yarn build: exit 0, no broken links surfaced by
onBrokenLinks: throw. Anchor warnings present are pre-existing on
master (community#superset-community-calendar) and unrelated.

docs/developer_docs_versioned_docs/version-6.1.0/testing/storybook.md

@@ -0,0 +1,114 @@
+---
+title: Storybook
+sidebar_position: 5
+---
+
+<!--
+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.
+-->
+
+# Storybook
+
+Superset uses [Storybook](https://storybook.js.org/) for developing and testing UI components in isolation. Storybook provides a sandbox to build components independently, outside of the main application.
+
+## Public Storybook
+
+A public Storybook with components from the `master` branch is available at:
+
+**[apache-superset.github.io/superset-ui](https://apache-superset.github.io/superset-ui/?path=/story/*)**
+
+## Running Locally
+
+### Main Superset Storybook
+
+To run the main Superset Storybook locally:
+
+```bash
+cd superset-frontend
+
+# Start Storybook (opens at http://localhost:6006)
+npm run storybook
+
+# Build static Storybook
+npm run build-storybook
+```
+
+### @superset-ui Package Storybook
+
+The `@superset-ui` packages have a separate Storybook for component library development:
+
+```bash
+cd superset-frontend
+
+# Install dependencies and bootstrap packages
+npm ci && npm run bootstrap
+
+# Start the @superset-ui Storybook (opens at http://localhost:9001)
+cd packages/superset-ui-demo
+npm run storybook
+```
+
+## Adding Stories
+
+### To an Existing Package
+
+If stories already exist for the package, extend the `examples` array in the package's story file:
+
+```
+storybook/stories/<package>/index.js
+```
+
+### To a New Package
+
+1. Add package dependencies:
+
+   ```bash
+   npm install <package>
+   ```
+
+2. Create a story folder matching the package name:
+
+   ```bash
+   mkdir storybook/stories/superset-ui-<package>/
+   ```
+
+3. Create an `index.js` file with the story configuration:
+
+   ```javascript
+   export default {
+     examples: [
+       {
+         storyPath: '@superset-ui/package',
+         storyName: 'My Story',
+         renderStory: () => <MyComponent />,
+       },
+     ],
+   };
+   ```
+
+   Use the `|` separator for nested stories:
+   ```javascript
+   storyPath: '@superset-ui/package|Category|Subcategory'
+   ```
+
+## Best Practices
+
+- **Isolate components**: Stories should render components in isolation, without application context
+- **Show variations**: Create stories for different states, sizes, and configurations
+- **Document props**: Use Storybook's controls to expose configurable props
+- **Test edge cases**: Include stories for loading states, error states, and empty states