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

Snapshots all four versioned Docusaurus sections at v6.1.0. Built on
top of the version-cutting tooling work in chore/docs-cut-6.1.0-versions
so the snapshot benefits from:

- Auto-gen refresh before snapshotting (database pages from engine
  spec metadata, API reference from openapi.json, component pages
  from Storybook stories) — captured at the SHA we cut from rather
  than whatever happened to be on disk.
- Data-import freeze: country list, feature flag table, database
  diagnostics, and component metadata are copied into snapshot-local
  `_versioned_data/` dirs so the historical version doesn't silently
  mutate when the source files change.
- Depth-aware import-path rewriter that handles deeply-nested
  component MDX files referencing `../../../src/` from the snapshot.

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.

The frozen `databases.json` in the snapshot is the canonical 80-database
artifact from the latest committed state in master (preserved by the
generator's input-hash cache), not a fallback regenerated from a
local Flask environment.

docs/developer_docs_versioned_docs/version-6.1.0/components/ui/buttongroup.mdx

@@ -0,0 +1,88 @@
+---
+title: ButtonGroup
+sidebar_label: ButtonGroup
+---
+
+<!--
+    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';
+
+# ButtonGroup
+
+ButtonGroup is a container that groups multiple Button components together with consistent spacing and styling.
+
+## Live Example
+
+<StoryWithControls
+  component="ButtonGroup"
+  props={{
+  expand: false
+}}
+  controls={[
+  {
+    name: "expand",
+    label: "Expand",
+    type: "boolean",
+    description: "When true, buttons expand to fill available width."
+  },
+  {
+    name: "className",
+    label: "Class Name",
+    type: "text",
+    description: "CSS class name for custom styling."
+  }
+]}
+  sampleChildren={[{"component":"Button","props":{"buttonStyle":"tertiary","children":"Button 1"}},{"component":"Button","props":{"buttonStyle":"tertiary","children":"Button 2"}},{"component":"Button","props":{"buttonStyle":"tertiary","children":"Button 3"}}]}
+/>
+
+## Try It
+
+Edit the code below to experiment with the component:
+
+```tsx live
+function Demo() {
+  return (
+    <ButtonGroup>
+      <Button buttonStyle="tertiary">Button 1</Button>
+      <Button buttonStyle="tertiary">Button 2</Button>
+      <Button buttonStyle="tertiary">Button 3</Button>
+    </ButtonGroup>
+  );
+}
+```
+
+## Props
+
+| Prop | Type | Default | Description |
+|------|------|---------|-------------|
+| `expand` | `boolean` | `false` | When true, buttons expand to fill available width. |
+
+## Import
+
+```tsx
+import { ButtonGroup } from '@superset-ui/core/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/ButtonGroup/ButtonGroup.stories.tsx).
+:::