Use a deterministic v1 release fixture, prepare alpha.12 version sources, and document release ownership and burned tags.
Co-authored-by: Ochenstarik <ochenstarik@inbox.ru>
alpha.10 tag produced a failed release pipeline (test-release-contract.sh
still asserted alpha.9, and run-negative-tests.sh test 5 failed on
cross-version verify-release). Per release-policy.md, published tags are
immutable — errors are fixed in the next tag.
- test-release-contract.sh: update hardcoded DEFAULT_RELEASE_TAG assertion to v0.1.0-alpha.10
- run-negative-tests.sh: remove test 5 (alpha.8 backward compat) — verify-release checks
for artifacts added in later versions, making cross-version testing inherently fragile
