Replaces the workflow_call to do-release with directly inlined release
and validate jobs. All steps now appear flat in the Actions UI with full
individual step visibility instead of being collapsed under a setup job.
Tag resolution in the release job is simplified: the tag always comes
from needs.prepare.outputs.tag, removing the detect-tag guessing needed
for standalone dispatch.
do-release.yml is unchanged and remains available for manual dispatch.
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