feat: add beliefs with evidence-derived confidence, contradictions and corrections

Phase 6. Beliefs are propositions with a prior set by epistemic kind and a
confidence computed from typed evidence: sigmoid(logit(prior) + slope ×
(support × diversity − opposition)), where support from a single source
is discounted so repetition cannot manufacture certainty, and bounds keep
the mind away from absolute certainty. Every evaluation stores its
breakdown and appends a version row protected by the append-only
trigger; the belief page shows the arithmetic, evidence for and against,
alternatives, contradictions and history.

Contradiction detection is deterministic first (negation plus token
overlap): a hit emits contradiction_detected, links both beliefs and
makes each counter-evidence for the other so both trend to contested.
Operators can assert beliefs (their statement is the evidence), add
evidence, mark a belief wrong (pinned rejected, history kept) and forbid
an inference; do-not-infer corrections block matching hypotheses.
Retracting a memory retracts the evidence that cited it and re-evaluates
the beliefs concerned.

The associate process proposes low-confidence causal hypotheses from
co-occurring notable observations, and the hypothesis handler turns
admitted ones into beliefs with automatic alternatives, closing demo
scenarios 1 and 2 without any model call.

internal/api/memory.go

@@ -232,6 +232,7 @@ func (s *Server) memoryRetract(w http.ResponseWriter, r *http.Request) {
 	}
 	s.deps.Events.OperatorAction(r.Context(), m.ID, actor(r), "memory.retract", "Operator "+actor(r)+" marked a memory inaccurate: "+in.Reason, map[string]any{"memory_id": id, "reason": in.Reason})
 	s.deps.Audit.Log(r.Context(), "memory.retract", "memory", id.String(), map[string]any{"reason": in.Reason})
+	s.propagateMemoryRetraction(r, m.ID, id)
 	w.WriteHeader(http.StatusNoContent)
 }
 
@@ -272,3 +273,18 @@ func trunc(s string, n int) string {
 	}
 	return s
 }
+
+// propagateMemoryRetraction stops a retracted memory counting as belief
+// evidence and re-evaluates the beliefs that cited it.
+func (s *Server) propagateMemoryRetraction(r *http.Request, mind, memoryID ids.ID) {
+	affected, err := s.deps.Beliefs.RetractEvidence(r.Context(), s.deps.DB, mind, "memory", string(memoryID))
+	if err != nil {
+		logger(r).Warn("retract evidence failed", "err", err)
+		return
+	}
+	for _, bid := range affected {
+		if _, err := s.deps.Beliefs.Reevaluate(r.Context(), s.deps.DB, s.Emitter(), mind, bid, "supporting memory retracted by operator"); err != nil {
+			logger(r).Warn("re-evaluate failed", "belief", bid, "err", err)
+		}
+	}
+}