raise minimum carb ratio to 3 g/U

because that's the lower limit used by oref at https://github.com/nightscout/Trio/blob/e98a71296e62f57bf004cb9c0c8d6135cb181f08/trio-oref/lib/profile/carbs.js#L16-L19

FreeAPS/Sources/Modules/CarbRatioEditor/CarbRatioEditorStateModel.swift

@@ -10,7 +10,7 @@ extension CarbRatioEditor {
 
         let timeValues = stride(from: 0.0, to: 1.days.timeInterval, by: 30.minutes.timeInterval).map { $0 }
 
-        let rateValues = stride(from: 1.0, to: 501.0, by: 1.0).map { ($0.decimal ?? .zero) / 10 }
+        let rateValues = stride(from: 30.0, to: 501.0, by: 1.0).map { ($0.decimal ?? .zero) / 10 }
 
         var canAdd: Bool {
             guard let lastItem = items.last else { return true }