fix(cron): apply timezone to all schedule kinds, not just cron

Move TZ application before schedule kind switch in MergeCronSchedule.
Ensure timezone applies consistently to cron, every, and at expressions.

internal/store/cron_store.go

@@ -237,6 +237,8 @@ func MergeCronSchedule(current CronSchedule, patch *CronSchedule) CronSchedule {
 	}
 
 	merged := CronSchedule{Kind: newKind}
+	// TZ: always use patch value for all schedule kinds. Empty = UTC (default).
+	merged.TZ = patch.TZ
 	switch newKind {
 	case "cron":
 		if patch.Expr != "" {
@@ -244,9 +246,6 @@ func MergeCronSchedule(current CronSchedule, patch *CronSchedule) CronSchedule {
 		} else if current.Kind == newKind {
 			merged.Expr = current.Expr
 		}
-		// TZ: always use patch value. Empty = UTC (default).
-		// Callers (UI, agent tool) send full schedule via spread, so empty is explicit.
-		merged.TZ = patch.TZ
 	case "every":
 		if patch.EveryMS != nil {
 			merged.EveryMS = patch.EveryMS
@@ -298,25 +297,25 @@ func ValidateCronSchedule(schedule *CronSchedule) error {
 func ApplyCronScheduleUpdates(updates map[string]any, schedule CronSchedule) {
 	updates["schedule_kind"] = schedule.Kind
 
+	// TZ applies to all schedule kinds (used for display and cron evaluation).
+	if schedule.TZ != "" {
+		updates["timezone"] = schedule.TZ
+	} else {
+		updates["timezone"] = nil
+	}
+
 	switch schedule.Kind {
 	case "cron":
 		updates["cron_expression"] = schedule.Expr
-		if schedule.TZ != "" {
-			updates["timezone"] = schedule.TZ
-		} else {
-			updates["timezone"] = nil
-		}
 		updates["interval_ms"] = nil
 		updates["run_at"] = nil
 	case "every":
 		updates["cron_expression"] = nil
-		updates["timezone"] = nil
 		updates["interval_ms"] = *schedule.EveryMS
 		updates["run_at"] = nil
 	case "at":
 		runAt := time.UnixMilli(*schedule.AtMS)
 		updates["cron_expression"] = nil
-		updates["timezone"] = nil
 		updates["interval_ms"] = nil
 		updates["run_at"] = runAt
 	}