Public: page views per guide slug (last N days) so the /guides index can auto-order by what people actually read. Guide page views are identified the same way /admin/guide-funnel does — source='guide' + ref='guide-<slug>' (the per-guide tracker tags them; the generic path field is NOT set on guide views, which is why a path-based match returns nothing). Only aggregates leave the backend.

Cached GUIDES_POPULARITY_TTL_SECONDS per days (#333). A failed read answers the last body, or an empty map when there has never been one: the only consumer (lmcp-web) already reads a failure as an empty map, and this route never answers 500 for a database hiccup.