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)

CHANGELOG.md

@@ -0,0 +1,28 @@
+# Changelog
+
+All notable changes to BEHAVE packages are documented here.
+Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
+Versions follow [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+---
+
+## [0.1.0] — 2026-05-17
+
+Initial public release of all three packages.
+
+### behave-core
+
+- Shared observation envelope and schema contract (`BehaveObservation`)
+- Pydantic v2 base models for domain-agnostic behavioral records
+
+### behave-shell
+
+- Shell-session behavioral observation registry
+- Primitive catalog covering command execution, session lifecycle, environment, and navigation events
+- Layered on `behave-core`
+
+### behave-text
+
+- Text/messaging-domain behavioral observation registry
+- Primitive catalog covering message composition, conversation, and metadata events
+- Layered on `behave-core`