feat: remember per-satellite doppler offset in calculator

Store the last entered offset (kHz) per satellite in SharedPreferences
via SettingsRepo, and restore it when the linear transponder calculator
is shown for that satellite.

Follows the project's MVI/clean architecture:
- ISettingsRepo: getSatelliteOffset / setSatelliteOffset
- SettingsRepo: backed by SharedPreferences
- RadarState: calculatorOffsetKHz field
- RadarAction: ChangeCalculatorOffset
- RadarViewModel: loads offset on SelectTransmitter, saves on change
- CalculatorPage/DopplerFrequencyCalculator: receive offset via params
instead of accessing SharedPreferences directly from the UI layer.

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/repository/ISettingsRepo.kt

@@ -75,4 +75,9 @@ interface ISettingsRepo {
     val radioControlSettings: StateFlow<RadioControlSettings>
     fun updateRadioControlSettings(settings: RadioControlSettings)
     //endregion
+
+    //region # Per-satellite calculator offset settings
+    fun getSatelliteOffset(catnum: Int): String
+    fun setSatelliteOffset(catnum: Int, offset: String)
+    //endregion
 }