release: bump all packages to 0.1.1, add PyPI metadata and CHANGELOG

- Add readme field to all three pyproject.toml files (populates PyPI description page)
- Bump versions to 0.1.1 and update behave-core pin in shell/text
- Update Install sections in root, BEHAVE-SHELL, and BEHAVE-TEXT READMEs to lead with pip install from PyPI
- Add CHANGELOG.md at project root (Keep-a-Changelog format)

core/pyproject.toml

@@ -4,8 +4,9 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "behave-core"
-version = "0.1.0"
+version = "0.1.1"
 description = "BEHAVE shared observation envelope — schema contract used by BEHAVE-SHELL and BEHAVE-TEXT"
+readme = "README.md"
 requires-python = ">=3.11"
 license = { text = "GPL-3.0-or-later" }
 authors = [{ name = "ANTI" }]