loop: add rule trace/explanation engine

ExplainTick and ExplainGate produce a full TickTrace for every tick,
recording per-rule: predicate result, gate result, first gate blocker,
gate detail (snooze/cooldown/presence etc.), and win/loss info.

IPC layer: new MethodTickTrace, DTOs (TickTrace, RuleTrace, GateDetail),
dispatch, client proxy, and CoreAPI interface method.

Daemon: tickLoop caches the latest trace; daemonAPI wraps storeAPI
with a TickTrace override that returns the cached trace.

Tests: 15 new tests for ExplainGate (all blockers, bypass conditions,
ordering) and ExplainTick (nothing fires, one fires, tiebreak,
winner/lost_to recording, gate-blocked recording).

internal/ipc/server.go

@@ -174,6 +174,10 @@ func (a *storeAPI) RevertFact(ctx context.Context, key string) (int64, error) {
 	return newID, mapErr(err)
 }
 
+func (a *storeAPI) TickTrace(ctx context.Context) (TickTrace, error) {
+	return TickTrace{}, errors.New("store: tick trace not available via direct store API")
+}
+
 func (a *storeAPI) ListTools(ctx context.Context, status string) ([]Tool, error) {
 	ts, err := a.s.ListTools(ctx, status)
 	if err != nil {
@@ -629,6 +633,13 @@ func (s *Server) dispatch(ctx context.Context, req Request) (json.RawMessage, er
 		}
 		return marshalResult(map[string]int64{"new_id": newID}), nil
 
+	case MethodTickTrace:
+		t, err := s.api.TickTrace(ctx)
+		if err != nil {
+			return nil, err
+		}
+		return marshalResult(t), nil
+
 	case MethodAssertStepUp:
 		if s.StepUp != nil {
 			return marshalResult(nil), s.StepUp(ctx)