Kyn MVP v2 Finish Tasks

These are the remaining tasks required to close out v2 cleanly.

1. Reporter and Release Correctness

Status: completed

• fix Docker multi-arch build correctness for arm64 image publishing
• ensure machine reporters only emit actionable failing diagnostics
• add tests covering machine reporter filtering behavior

2. Distribution Verification and Release Docs

Status: completed

• strengthen CI/release coverage for publishable artifacts
• clarify release/install story across binaries and container image usage
• close the remaining portability/documentation gaps for the v2 contract

3. Presets and Adoption Polish

Status: completed

• expand kyn init --preset beyond web-ui
• add docs/examples for web-ui, api, proto, and iac
• finish the final v2 adoption polish across README and docs