Fleet readiness for an AI observer

Returns the fleet readiness aggregate projected for an Observe Only token: per-node domain cells, the findings behind them, state and severity counts, and a staleness flag. Findings are capped at 50, worst first. The control domain is withheld from this surface and named in domainsOmitted. The aggregate is cached for up to 15 seconds and shared across callers, so generatedAt and each cell's evidenceAgeMs describe the age of the evidence, not of the request. Dismissals applied in the Fleet Readiness view are not read here, because reading them would mutate dismissal state. This is one of the five paths an Observe Only token may reach. Requires node:read permission.