Agent Skills: ring:validating-acceptance-criteria

Validating a completed task against its acceptance criteria, mapping each AC to evidence, and gating completion on explicit user sign-off (self-approval prohibited). Gate 5 of ring:running-dev-cycle / ring:running-dev-cycle-frontend, run at task cadence after ring:reviewing-code. Use when implementation and tests are done and you need approval to close the task. Skip outside a dev-cycle, or for doc-only or non-code tasks.