shepherd-driver - per-PR drive-to-merge convergence loop

This SKILL.md is the natural-language module derived from a genesis design packet; refactors re-run the genesis skill from that packet.

This skill is a COMPOSED BUILDING BLOCK, not a user-facing entrypoint. It was extracted (genesis R3 EXTRACT) from batch-bug-shepherd when a second consumer (apm-issue-autopilot) needed the same per-PR convergence loop. Both orchestrators COMPOSE this skill; neither re-implements the loop. It in turn COMPOSES the apm-review-panel skill for the review pass -- it does NOT re-implement panel review.

Boundary (what this skill does and does NOT do)

DOES: take ONE PR that already exists and drive it to a terminal landing-ready state; resolve cross-PR merge conflicts; emit the PR-facing advisory and supersede comments; return a schema-valid completion_return.