feat(research): ablations, broadcast and self-model experiments, counterfactuals

A framework for testing functional properties of the architecture
(Part C). None of it claims consciousness; every measure has an
operational definition in research.Measures.

- Ablations (attention, memory retrieval, affect, metacognition,
  commitments, volition, global workspace, curiosity, association, goals,
  narrative, notifications) and workspace overrides (force a matching
  candidate in or out of admission) live in a fork's cognitive
  configuration. Original minds refuse them on create and update; only
  snapshot restores may carry them, so they are part of the configuration
  digest. Excluded candidates are recorded with fate "excluded".
- Self-model experiments override a fork's self-model (capabilities,
  identity, goals, knowledge gaps) without touching policy. When an
  action's effective policy disagrees with the self-model, cognition
  records a self_model_mismatch and corrects the entry; experiments report
  self-model accuracy and correction latency.
- Counterfactual experiments replay a mind's recorded stimuli from a
  snapshot with chosen events omitted; the report lists what differed in
  beliefs, wants, intentions, memories, attention and capability
  decisions, in a form introspection can cite.
- Experiments record a protocol (kind, independent variable, controlled
  variables, measures), per-variant volition, plan, downstream-by-category
  (events reachable from each stimulus through recorded links),
  introspection and self-model measures and event ranges; comparisons add
  want, intention and plan-capability overlap, measure ranges, a
  descriptive architecture share and a downstream delta; reproducibility
  is labelled against the previous run of the same definition.
- research.Agency computes want→intention, intention→action, abandonment,
  commitment fulfilment and conflict, blocked intentions, replanning,
  outcome success and introspection accuracy; MetacognitiveCalibration
  relates confidence and expressed uncertainty in replies to later belief
  revision, with Brier scores for each half of the period.
- The sandbox test harness gains volition, planning, agency and research
  but not the motivation hook, whose wall-clock decay would make replay
  comparisons timing-dependent.

internal/replay/replay.go

@@ -270,6 +270,10 @@ func (s *Service) Execute(ctx context.Context, r Replay) (Replay, error) {
 // perceptions (messages, integrations, observations) and operator actions.
 var StimulusCategories = []events.Category{events.CatPerception, events.CatOperator}
 
+// IsStimulus reports whether an event reached the mind from outside and so
+// is replayed as input (experiments reuse the same selection).
+func IsStimulus(e events.Event) bool { return isStimulus(e) }
+
 func isStimulus(e events.Event) bool {
 	if strings.HasPrefix(e.Source, "brain") {
 		return false