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/extensions/overview.md

@@ -0,0 +1,59 @@
+---
+title: Overview
+sidebar_position: 1
+---
+
+<!--
+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.
+-->
+
+# Overview
+
+Apache Superset's extension system enables organizations to build custom features without modifying the core codebase. Inspired by the [VS Code extension model](https://code.visualstudio.com/api), this architecture addresses a long-standing challenge: teams previously had to fork Superset or make invasive modifications to add capabilities like query optimizers, custom panels, or specialized integrations—resulting in maintenance overhead and codebase fragmentation.
+
+The extension system introduces a modular, plugin-based architecture where both built-in features and external extensions use the same well-defined APIs. This "lean core" approach ensures that any capability available to Superset's internal features is equally accessible to community-developed extensions, fostering a vibrant ecosystem while reducing the maintenance burden on core contributors.
+
+## What are Superset Extensions?
+
+Superset extensions are self-contained `.supx` packages that extend the platform's capabilities through standardized contribution points. Each extension can include both frontend (React/TypeScript) and backend (Python) components, bundled together and loaded dynamically at runtime using Webpack Module Federation.
+
+## Extension Capabilities
+
+Extensions can provide:
+
+- **Custom UI Components**: New panels, views, and interactive elements
+- **Commands and Menus**: Custom actions accessible via menus and keyboard shortcuts
+- **REST API Endpoints**: Backend services under the `/extensions/` namespace
+- **MCP Tools and Prompts**: AI agent capabilities for enhanced user assistance
+
+## UI Components for Extensions
+
+Extension developers have access to pre-built UI components via `@apache-superset/core/components`. Browse all available components on the [UI Components](/developer-docs/components/) page and filter by **Extension Compatible** to see components available to extensions.
+
+## Next Steps
+
+- **[Quick Start](./quick-start)** - Build your first extension with a complete walkthrough
+- **[Architecture](./architecture)** - Design principles and system overview
+- **[Dependencies](./dependencies)** - Managing dependencies and understanding API stability
+- **[Contribution Types](./contribution-types)** - Available extension points
+- **[Development](./development)** - Project structure, APIs, and development workflow
+- **[Deployment](./deployment)** - Packaging and deploying extensions
+- **[MCP Integration](./mcp)** - Adding AI agent capabilities using extensions
+- **[Security](./security)** - Security considerations and best practices
+- **[Tasks](./tasks)** - Framework for creating and managing long running tasks
+- **[Community Extensions](./registry)** - Browse extensions shared by the community