Add address-findings skill

Add a skill that addresses the review findings on an Entire trail: given a trail URL or number, it fetches the trail's open findings, fixes the code in the current worktree (applying suggested diffs or hand-editing), and resolves each one on the trail. Ambiguous findings are left open and reported.

The skill orchestrates existing entire trail finding commands; no CLI changes are needed. README and using-entire router entries are intentionally omitted so the unreleased findings feature is not publicly advertised until release.