docs-sync -- per-PR documentation impact panel

The docs corpus drifts silently and constantly. This skill catches drift at PR-open time, classifies its impact, and orchestrates a persona panel to produce a patch-ready advisory comment.

The pattern is A1 PANEL + B1 FAN-OUT/SYNTHESIZER + A8 ALIGNMENT LOOP. The classifier is the cost gate (~70% of PRs short-circuit to no-change with ~1 LLM call). When the panel does fan out, every agent reads a bounded context (~10 KB) -- never the full corpus.

This skill is ADVISORY. It does not gate merge, apply verdict labels, or push to the contributor's fork. The orchestrator is the sole writer to the PR: exactly one comment per run (idempotent edit-in-place), plus optional label sweeps.

Architecture invariants