Retag release as 0.4.2 to match Chatto server version

Establish a versioning policy: chattolib's PyPI version follows the
targeted Chatto server version (0.4.2 targets Chatto 0.4.2). Use
.postN suffixes for chattolib-only fixes between server releases.

Documented in CLAUDE.md; README refreshed to drop the 1.0.0a1
pre-alpha label.

1.0.0a1 was uploaded to PyPI in error; it should be yanked via the
PyPI web UI so pip prefers 0.4.2.

CLAUDE.md

@@ -8,6 +8,10 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 
 **chattolib** is an async Python client library for the [Chatto](https://chat.chatto.run) webchat Connect API (`https://chat.chatto.run/api/connect/…`). Chatto migrated from GraphQL to protobuf-first ConnectRPC in v0.4.x (see [ADR-042](https://github.com/chattocorp/chatto/blob/main/docs/adr/ADR-042-protobuf-first-public-api.md), which supersedes ADR-003). This library speaks Connect JSON over HTTP for all request/response operations.
 
+## Versioning
+
+**chattolib's version tracks the Chatto server version it targets.** A new Chatto release triggers a matching chattolib release (e.g. Chatto `0.4.2` → chattolib `0.4.2`). If a chattolib-only fix is needed between server releases, use a post-release suffix (`0.4.2.post1`) rather than bumping the base number ahead of Chatto.
+
 ## Build & Development
 
 ```bash

README.md

@@ -2,11 +2,11 @@
 
 **Unofficial** async Python client library for the [Chatto](https://chat.chatto.run) webchat API.
 
-> **Pre-alpha (1.0.0a1)** — targets Chatto 0.4.x's ConnectRPC API. The
-> upstream server dropped GraphQL in favour of a protobuf-first Connect API
-> (see ADR-042 in chattocorp/chatto), and this release is a full rewrite for
-> that transport. The library speaks Connect JSON over HTTP; realtime
-> WebSocket support is a follow-up.
+> Chattolib versions track the Chatto server version they target. **0.4.2**
+> targets Chatto 0.4.2's ConnectRPC API. The upstream server dropped GraphQL
+> in favour of a protobuf-first Connect API (see ADR-042 in chattocorp/chatto),
+> and this release is a full rewrite for that transport. The library speaks
+> Connect JSON over HTTP; realtime WebSocket support is a follow-up.
 
 ## Install
 

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "chattolib"
-version = "1.0.0a1"
+version = "0.4.2"
 description = "Async Python client library for the Chatto webchat Connect API"
 requires-python = ">=3.11"
 license = "MIT"