Bump version to 0.4.0

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Add kojin-amqp and kojin-dashboard to publish workflow

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

v0.2.0: Workflows, scheduling, and result backends

Prepare v0.1.0 for crates.io release

Add workspace and per-crate metadata (authors, description, keywords,
categories, homepage, documentation, readme), version-pin path
dependencies for cargo publish, rewrite README with badges and quick
start, add module-level doc comments, CHANGELOG.md, and CI/publish
GitHub Actions workflows.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>