feat: keep mutual state across nav + overlay station-B track on main radar

- MutualViewModel is Activity-scoped, so returning from Radar keeps query results
- TrackSampleData gains time field for live cut-off
- Removed standalone mutual card from radar page
- RadarViewCompose draws optional dashed station-B track + current dot
- RadarScreen builds trackB from mutual data up to current time

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

@@ -56,6 +56,7 @@ data class MutualPassData(
 
 /** Minimal track sample for cross-module sharing (angles in degrees). */
 data class TrackSampleData(
+    val time: Long = 0L,
     val azimuthA: Double,
     val elevationA: Double,
     val azimuthB: Double,