v0.5.1

feat: Update readme and changelog with version 0.5.1

v0.4.0

Full Changelog: v0.3.0...v0.4.0

docs: update CHANGELOG and README for v0.3.0 release

- CHANGELOG: replace [0.2.1] with [0.3.0] entry; merge FEAT-023
  (ConfigurationRegistry + Kiro + whiteboard polish) with backlog
  clearance items into a single release note.
- README: add version badge (0.3.0), VS Code compatibility badge,
  and Marketplace/Releases download instructions.