Fail coordinated GitHub tag validation before package builds

[PrzemyslawKlys]

Summary

• reject non-retry-safe coordinated GitHub tag settings before package builds, signing, checkpoint creation, or remote publication
• keep the later version-aware preflight for mixed-version release plans
• preserve non-publishing gates and completed operations when resuming an incomplete release
• explain how to choose a stable version-based tag in the failure message

Validation

• coordinated-release test suite: 95 passed
• focused volatile-tag and Build-gate regressions: 2 passed
• independent local review completed; two resume/gate findings were fixed and confirmed