feat(beliefs): source reliability by domain, never global

A source's track record is kept per (evidence family, belief subject) and
updated only by outcomes: predictions derived from a belief resolving, and
operators marking a belief wrong. With three or more outcomes in a domain
the record adjusts the credibility of that source's new evidence in that
domain, and the adjustment is written on the evidence row. Standing in one
domain never moves standing in another, and the trust-level credibility
constants are never rewritten. Migration 0021 is additive; belief pages
show each cited family's record in the belief's domain.

internal/api/beliefs.go

@@ -141,8 +141,9 @@ type BeliefDetail struct {
 	Assertions   []epistemics.Assertion `json:"assertions"` // who stated this proposition, with what stance
 	// Score semantics: the raw number, its empirical reading where prediction
 	// outcomes allow one, and the strongest deterministic reason to doubt it.
-	Calibration        beliefs.Calibrated `json:"calibration"`
-	PrimaryUncertainty string             `json:"primary_uncertainty"`
+	Calibration        beliefs.Calibrated          `json:"calibration"`
+	PrimaryUncertainty string                      `json:"primary_uncertainty"`
+	Reliability        []beliefs.SourceReliability `json:"reliability"` // each cited family\'s record in this belief\'s domain
 }
 
 // BeliefDetail assembles the detail; shared with the UI.
@@ -174,6 +175,10 @@ func (s *Server) BeliefDetail(r *http.Request, mind, id ids.ID) (BeliefDetail, e
 		d.Calibration = beliefs.CalibrateWith(b.Confidence, nil)
 	}
 	d.PrimaryUncertainty = beliefs.PrimaryUncertainty(d.Breakdown, d.Evidence)
+	d.Reliability = s.deps.Beliefs.ReliabilityFor(ctx, mind, b, d.Evidence)
+	if d.Reliability == nil {
+		d.Reliability = []beliefs.SourceReliability{}
+	}
 	d.Events, _ = s.deps.Events.DerivedFrom(ctx, "belief", string(id), 100)
 	if !b.OriginEvent.IsZero() {
 		if e, err := s.deps.Events.Get(ctx, b.OriginEvent); err == nil {