task: label-consolidation - Build the Stage 3 and 4 consolidation tool #3822

Summary

Spec 008 Stages 3 and 4 need a tool that renames, creates and relabels labels across the organisation and, only after per-repository approval, deletes the labels outside the approved set. It does not exist yet (tasks T062, T062b, T062c, T065 and T065a).

Scope

• Dry run by default; changes only with --apply and --confirm-gate.
• Run lock with epochs, resume and abandon; append-only intended/done log; idempotent re-runs.
• Stage 4 deletes only after @ashleyshaw approval verifies and the repository still matches its dry run.
• Private repositories keep their dry run, log, approval and gate comments out of this public repository (decision of 2026-10-04).

Not in scope

Running the tool against the organisation (T063, T064, T066, T067) and the Linear stages.