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

- Snapshot all four versioned docs sections at v6.1.0; master continues to
  serve as "Next" (lastVersion: current, banner: unreleased) so editing
  master keeps updating the canonical URLs
- Enable the previously-disabled components plugin and version it
- Rename stale "developer_portal" references to "developer_docs" across
  package.json scripts, manage-versions.mjs, theme files (DocVersionBadge,
  DocVersionBanner), DOCS_CLAUDE.md, and README.md (URL backward-compat
  redirect /developer_portal/* preserved)
- Add admin_docs version scripts; drop dead "tutorials" plugin id from
  the version badge
- Generalize fixVersionedImports in manage-versions.mjs to walk every
  section's snapshot and rewrite ../../src/ and ../../data/ imports,
  catching admin_docs and components files that previous version cuts
  would have broken
- Remove orphan files: developer_portal_versions.json,
  tutorials_versions.json, and stray empty versions.json files inside
  components/ and developer_docs/ content directories

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

@@ -0,0 +1,61 @@
+---
+title: Frontend Testing
+sidebar_position: 2
+---
+
+<!--
+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.
+-->
+
+# Frontend Testing
+
+🚧 **Coming Soon** 🚧
+
+Comprehensive guide for testing Superset's frontend components and features.
+
+## Topics to be covered:
+
+- Jest configuration and setup
+- React Testing Library best practices
+- Component testing strategies
+- Redux store testing
+- Async operations and API mocking
+- Snapshot testing guidelines
+- Coverage requirements and reporting
+- Debugging test failures
+- Performance testing for UI components
+
+## Quick Commands
+
+```bash
+# Run all frontend tests
+npm run test
+
+# Run tests in watch mode
+npm run test -- --watch
+
+# Run tests with coverage
+npm run test -- --coverage
+
+# Run specific test file
+npm run test -- MyComponent.test.tsx
+```
+
+---
+
+*This documentation is under active development. Check back soon for updates!*