Add skill to review product backlog

This page is a capture in the discarded bucket of the product backlog.

Resolved (deep backlog refinement, 2026-07-11): doc/llm/skills/agile-refine-backlog exists: 'Run a backlog housekeeping session: scan the next/deferred captures, clarify descriptions, cull stale items, and re-prioritise between buckets.' – matches the capture's request.

We could get claude to review the stories, add more details, etc. Needs more thinking.