v0.1.1

Add reusable GitHub Action, self-test workflow, and rewrite README

Packages wit-breaking as a composite GitHub Action (uses: jayblast-spec/
wit-breaking@main) -- the actual adoption path for a CI-shaped tool like
this, and one that needs no npm publish since Actions distribute via git.
Added a real self-test workflow that exercises the action end-to-end
against known breaking and non-breaking fixtures (using GitHub's local
action reference support, uses: ./) rather than trusting the YAML by eye.
README rewritten to explain WIT and the Component Model from scratch for
readers unfamiliar with either, walk through why breaking changes matter
here, and be explicit about every design tradeoff and why it was made.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>