* fix(ci): retarget label docs at triage.yml and guard label declarations
.github/labels.yml still described the auto-labeling setup as the three
workflows triage.yml replaced (pr-labeler.yml / pr-triage.yml /
issue-triage.yml), and its section headers pointed at the deleted
.github/labeler.yml and pr-triage.yml. A reader following those pointers
lands on 404s.
The same pair had an unguarded failure mode: triage.yml applies labels by
name, and GitHub rejects the whole addLabels batch with 422 when any name is
missing from the repository. Nothing checked that a label added to the
workflow also reached the declarative source of truth.
Point the comments at triage.yml and add scripts/check_label_declarations.py,
which fails when the workflow applies a label labels.yml does not declare.
* fix(ci): trace applied labels and cover the declaration guard
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Co-authored-by: Willem Jiang <willem.jiang@gmail.com>
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