[helly25]

BCR's recursive dependency build loads tests whose development-only fixture repository is unavailable. Build the public libraries as an external dependency and run the full test suite from the release root, preserving development dependencies.

AG;DR

• Keep Bazel 7/8/9 across Linux, macOS, and Windows for both consumer builds and full root tests. No validation gates are disabled.
• Synchronize the release template with the fix pushed to mboworks_bzl@0.8.0 bazelbuild/bazel-central-registry#11173 for 0.8.0. Document the two test contexts.
• Start 0.8.1 development after the 0.8.0 tag; README remains on published 0.8.0. No new release is created.
• Validation: all 182 Bazel tests and focused pre-commit checks passed. The published 0.8.0 archive also passed an anonymous consumer build using the registry metadata and all 182 root tests.
• The registry repair is independent and already pushed; it does not require this PR to merge first.