v0.6.4 — digest names the rotation target and health result

The morning digest now prints, under レーン統計, one line per lane artifact: 'review rotation: (previous <night|none>, refresh <ok|failed|skipped>)' from lane_N/rotation.json and 'health: runner=… result=… failures=n/m[ reason=…]' from lane_N/health.json (#69). Present-but-broken artifacts print 'unreadable (lane_N)'; artifact-free nights render exactly as before. Strings capped at 120 chars; empty identifiers and symlinked lane dirs are refused fail-visibly. Seats: GLM 5.3 / Opus 5 / Grok 4.6 cumulative GO. PR #27 squash 223511f (-dev#70).