docs: cut 6.1.0 versions for user_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), broken-internal-
links fix (#40102), and user_docs rename (#40171) all landed. With
the rename in place, all four sections now produce parallel-named
files at the docs/ root (no more bare `versioned_docs/` outlier).

Versioning behavior: lastVersion stays at current for every section,
so the canonical URLs (/user-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.

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:
    user_docs_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.
- developer_docs/extensions/overview.md snapshot has the FIXED
  ./mcp.md form (from #40102), so the SPA-nav 404 isn't baked into
  the 6.1.0 version.

Verified via full yarn build: exit 0, no broken links surfaced by
onBrokenLinks: throw.

docs/developer_docs_versioned_docs/version-6.1.0/api/get-all-available-domains.api.mdx

@@ -0,0 +1,58 @@
+---
+id: get-all-available-domains
+title: "Get all available domains"
+description: "Get all available domains"
+sidebar_label: "Get all available domains"
+hide_title: true
+hide_table_of_contents: true
+api: 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
+sidebar_class_name: "get api-method"
+info_path: developer-docs/api/superset
+custom_edit_url: null
+hide_send_button: true
+show_extensions: true
+---
+
+import MethodEndpoint from "@theme/ApiExplorer/MethodEndpoint";
+import ParamsDetails from "@theme/ParamsDetails";
+import RequestSchema from "@theme/RequestSchema";
+import StatusCodes from "@theme/StatusCodes";
+import OperationTabs from "@theme/OperationTabs";
+import TabItem from "@theme/TabItem";
+import Heading from "@theme/Heading";
+import Translate from "@docusaurus/Translate";
+
+<Heading
+  as={"h1"}
+  className={"openapi__heading"}
+  children={"Get all available domains"}
+>
+</Heading>
+
+<MethodEndpoint
+  method={"get"}
+  path={"/api/v1/available_domains/"}
+  context={"endpoint"}
+>
+
+</MethodEndpoint>
+
+
+
+Get all available domains
+
+<ParamsDetails>
+
+</ParamsDetails>
+
+<RequestSchema
+  {...require("./get-all-available-domains.RequestSchema.json")}
+>
+
+</RequestSchema>
+
+<StatusCodes
+  {...require("./get-all-available-domains.StatusCodes.json")}
+>
+
+</StatusCodes>