[samuel-williams-shopify]

Adds integration tests for release preparation, merge verification, ruleset creation and updates, publishing environment checks, unsigned builds, and the public Bake tasks. Git and Bake run against a separate consumer repository; GitHub transport is substituted at the boundary.

Follows the Sus layout under test/bake/gem/github/, with publisher-specific cases under publisher/. Uses Sus::Shared, lazy fixtures, temporary-directory and isolated Ruby contexts. Signing environment changes stay in child processes so parallel tests do not interfere.

Adds the unmodified bake-modernize test-coverage and documentation-coverage workflows, plus bake-test. Updates the checked-in required-check configuration and payload to match their standard job names. The live checks ruleset has also been updated to these names; all required checks pass.

Validation: 74 tests / 217 assertions pass; all 333 executable library/task lines are covered through standard Covered integration, and covered:validate passes. RuboCop and public API documentation coverage pass. Installed published v0.0.5 into a separate consumer bundle and exercised setup, branch preparation, regeneration validation, and unsigned packaging.

Addresses follow-up 1 from issues.md, including the requested standard coverage workflows. No production Ruby behavior changes.