🔖 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

README.md

@@ -1,5 +1,15 @@
 # Cereale
 
+> **This is the 1.x maintenance line**, which uses TypeScript's legacy
+> `experimentalDecorators`. It is feature-complete and supported for bug fixes.
+>
+> **New projects should use 2.x**, which moves to TC39 standard decorators and gains
+> compile-time checking of validation rules against field types — `@IsString() age: number`
+> becomes a compile error rather than a runtime surprise.
+>
+> Stay on 1.x if your toolchain transpiles with **oxc**, which does not yet implement the
+> standard decorator transform. `tsc` and esbuild both do, so most projects can move.
+
 Cereale is a lightweight TypeScript library that provides Spring-like decorators for JSON mapping and validation. Built with ZERO external dependencies, it simplifies the process of converting between plain JSON and class instances with full validation support.
 
 ## Features