0.5.0 — credibility floor

Dependency PRs green again (fork-aware privacy gate), the pin-drift root-cause fix, community intake, onboarding that reaches a green verification, the worked reconcile and producer signing recipes (mirror-tested), the federation envelope example, a grouped hexdocs sidebar, and a CI compatibility job on the previous supported Elixir/OTP pair. Corpus and registry unchanged at 94 cases. Attached: the standalone verification kit (verifier + conformance corpus) — the exact bytes the release gates verified.