🔖 chore: establish the 1.x legacy-decorator maintenance line

The 2.x README tells projects on an oxc-based toolchain to stay on 1.x, but no
such line existed — this branch point was version 0.1.0, so the advice pointed
at nothing installable.

- version 1.0.0
- CI runs on this branch as well as main and develop
- README opens with a maintenance-line notice pointing new projects at 2.x and
  naming the one reason to stay here: oxc does not implement the TC39 standard
  decorator transform, while tsc and esbuild do
- CHANGELOG names the release

No functional change: the code is exactly the state merged as PR #3.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SAcqrz3FcadkYr3xG32CjK

CHANGELOG.md

@@ -5,7 +5,13 @@ All notable changes to this project are documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## [Unreleased]
+## [1.0.0] - 2026-08-05
+
+The legacy-decorator line, promoted from 0.1.0 and now maintained in parallel with 2.x.
+Functionally identical to the previous unreleased state; only the version and the
+maintenance-line notice changed. See the 2.x branch for standard decorators and
+compile-time rule checking.
+
 
 ### Added