docs: add README, CONTRIBUTING, and CHANGELOG

- README with project overview, architecture diagram, and quick start
- CONTRIBUTING with development setup and code style guidelines
- CHANGELOG starting at 0.1.0 (unreleased, under active development)

CHANGELOG.md

@@ -0,0 +1,21 @@
+# Changelog
+
+## [0.1.0] — Unreleased
+
+### Added
+
+- Device registration, heartbeat, and update-check polling API
+- Artefact upload with SHA-256 integrity verification
+- Deployment management with target resolution (all, group, device)
+- Gated rate-limited download endpoint with HTTP Range support
+- JAR delta generation (BSDiff-style binary diff and patch packaging)
+- JWT authentication with admin user CRUD
+- React admin panel (dashboard, versions, deployments, users)
+- PostgreSQL auto-migration and auto-create database
+- OpenAPI 3.0 specification for daemon-facing endpoints
+
+### Changed
+
+- N/A (initial release under active development)
+
+[0.1.0]: https://github.com/onixbyte/pipely/tree/v0.1.0