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

feature/mutual/src/main/java/com/rtbishop/look4sat/feature/mutual/MutualScreen.kt

@@ -329,6 +329,7 @@ private fun MutualContent(
                 samples = pass.elevationSamples,
                 trackSamples = pass.trackSamples.map {
                     TrackSampleData(
+                        time = it.time,
                         azimuthA = it.azimuthA,
                         elevationA = it.elevationA,
                         azimuthB = it.azimuthB,