Support exceptional packaging revision tags

[unitmatrix]

Summary

• accept manually created release tags with an optional -rN packaging revision
• keep automatic upstream release tags matched exactly to the upstream version
• publish revisioned GHCR tags and GitHub Release metadata while verifying the unchanged upstream version
• document packaging revisions as an exceptional recovery for deleted immutable releases

For the current recovery, this enables xh/v0.26.2-r1 and age/v1.3.1-r1.

Validation

• accepted and rejected tag-format tests
• git diff --check
• release and tag workflow YAML parsing
• metadata validation for age and xh