Update Tasks extension docs to reflect official MCP status (#13)

* Initial plan

* docs: remove outdated experimental wording for tasks extension

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

Author: Copilot

MAINTAINERS.md

@@ -1,6 +1,6 @@
 # Tasks Extension Maintainers
 
-This document lists the maintainers of the MCP Tasks experimental extension.
+This document lists the maintainers of the MCP Tasks extension.
 
 This extension is maintained by the **Agents Working Group**.
 

README.md

@@ -1,7 +1,5 @@
-# MCP Tasks Extension (Experimental)
-This repository is under development and is working towards implementing the changes described in [SEP-2663](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2663). For the latest status and discussion, see the pull request.
-
-> **⚠️ Experimental Extension** — This repository contains an **experimental** extension to the [Model Context Protocol](https://modelcontextprotocol.io). It is **not** an official extension and may change significantly or be discontinued. See the [Extensions specification](https://modelcontextprotocol.io/seps/2133-extensions) for details on the experimental extension process.
+# MCP Tasks Extension
+This repository contains the official [Model Context Protocol](https://modelcontextprotocol.io) Tasks extension (`io.modelcontextprotocol/tasks`), based on [SEP-2663](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2663).
 
 ## Overview