docs(agent-email): fold the playground + autoCleanup notes into 0.2.1

0.2.1 hasn't been released yet, so there's no separate [Unreleased] bucket — the
one-command playground launcher and automatic sidecar cleanup ship in 0.2.1.
Moved both Added bullets under 0.2.1 and updated its intro (it's no longer a
docs-only release).

Author: kovtcharov

hub/agents/npm/agent-email/CHANGELOG.md

@@ -5,7 +5,11 @@ follows [SemVer](https://semver.org/): the **MAJOR** of the on-the-wire
 `SCHEMA_VERSION` is what `checkVersion` enforces at startup, so a contract MAJOR
 bump is always at least a package MINOR bump with a migration note.
 
-## [Unreleased]
+## 0.2.1
+
+Adds the one-command `playground` launcher and automatic sidecar cleanup, and
+makes this README the single canonical agent README (hub + npm). No wire-contract
+change (`SCHEMA_VERSION` stays `2.0`).
 
 ### Added
 
@@ -23,12 +27,6 @@ bump is always at least a package MINOR bump with a migration note.
   graceful, awaited path. A hard `SIGKILL` of the host process is the one case no
   in-process handler can catch.
 
-## 0.2.1
-
-Documentation/packaging release — no client API or wire-contract change
-(`SCHEMA_VERSION` stays `2.0`). Republishes so the live hub catalog picks up the
-current README.
-
 ### Changed
 
 - **This README is now the single canonical agent README** (hub + npm). The