Liveness + release/counts + corpus freshness

Liveness, plus whether the semantic corpus is a current picture of its sources.

notes follows the same contract as the site's /api/admin/health: a list of plain-language problems, each naming its own fix, EMPTY WHEN HEALTHY. That is what lets an existing probe consume this without new parsing logic.

This exists because a diagnostic nobody reads is documentation, not monitoring. The semantic index sat three months stale and breeds-only behind a publicly advertised RPC, and nothing anywhere would have said so.