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/brain/process.go

@@ -9,6 +9,7 @@ import (
 	"time"
 
 	"github.com/andydixon/noema/internal/attention"
+	"github.com/andydixon/noema/internal/beliefs"
 	"github.com/andydixon/noema/internal/memory"
 	"github.com/andydixon/noema/internal/minds"
 	"github.com/andydixon/noema/internal/workspace"
@@ -66,8 +67,9 @@ type State struct {
 
 // Services are read handles processes may use. Extended per phase.
 type Services struct {
-	Events EventReader
-	Memory *memory.Store
+	Events  EventReader
+	Memory  *memory.Store
+	Beliefs *beliefs.Store
 }
 
 // EventReader is the subset of the event store processes may call.