docs(experimental): list code-runtime-python in the group README; state the portable note as current fact

The review's items: the experimental group README's Packages table and Summary
now list code-runtime-python (CPython subprocess backend, ctx.codeRuntime),
paired; the portable-identifier note's Scope drops the 'has since shipped …
now lists' change narration in favor of the current state, removing the
apparent contradiction with 'the worker is the only shipped backend'.

packages/experimental/README.md

@@ -9,7 +9,7 @@ English | [中文](README.zh.md)
 
 ## Summary
 
-The experimental group contains prototype capabilities that are not part of any official release: they run on the real harness, but their contracts can change and they carry no support promise. The group holds Agent Teams, the cross-realm Inspector, and the browser-worker runtime and image packer used by preview deployments. Use these packages to try an unreleased capability; they carry no stability promise, and released products must not depend on them.
+The experimental group contains prototype capabilities that are not part of any official release: they run on the real harness, but their contracts can change and they carry no support promise. The group holds Agent Teams, the cross-realm Inspector, the CPython subprocess backend for the code-execution seam, and the browser-worker runtime and image packer used by preview deployments. Use these packages to try an unreleased capability; they carry no stability promise, and released products must not depend on them.
 
 ## Table of Contents
 
@@ -28,6 +28,7 @@ The experimental group contains prototype capabilities that are not part of any
 | [`agent-team`](agent-team/README.md) | Named teammates with durable messages and a shared task board | `ctx.agentTeams` |
 | [`agent-team-web-profile`](agent-team-web-profile/README.md) | Explicit source-checkout Web layer for Agent Teams | — |
 | [`client-ui-agent-team`](client-ui-agent-team/README.md) | Team roster, task board, and teammate navigation for Web | — |
+| [`code-runtime-python`](code-runtime-python/README.md) | CPython subprocess backend for the code-execution seam | `ctx.codeRuntime` |
 | [`inspector`](inspector/README.md) | Cross-realm CDP hub for Host debugging, Client Runtime inspection, network capture, and Cordis trees | `ctx.inspector` |
 | [`tool-agent-team`](tool-agent-team/README.md) | Ten tools that let the model create, message, and coordinate teammates | registers scoped tools on `ctx.tools` |
 | [`webworker-packer`](webworker-packer/README.md) | Builds the gzip-compressed VFS image consumed by the browser worker preview | library and CLI — no ctx key |