feat(map): multiple marked stations per grid with pin-to-top

- MarkedStation storage upgraded to an ordered list per grid
  (Map<String, List<MarkedStation>>); JSON array shape with legacy
  v14.1 single-object migration on read
- MapAction: SetMarkedStation appends (duplicate callsign ignored),
  RemoveMarkedStation deletes by callsign, PinMarkedStation moves a
  mark to the top of the list
- MaidenheadGridOverlay: red fill for any marked grid unchanged;
  first-call label mode shows the FIRST (pinned) marked callsign
- MapScreen: one row per mark (pale-yellow callsign), pin icon
  (冖 + stroke ↑, drawn in-app) left of the Marked label — shown only
  when the grid has 2+ marks; pinned row's icon grey, others pale
  yellow; delete icon per row
- New ic_pin.xml vector drawable; strings grid_mark_pin

feature/mutual/src/test/java/com/rtbishop/look4sat/feature/mutual/Fakes.kt

@@ -115,8 +115,8 @@ class FakeSettingsRepo(initialPosition: GeoPos = GeoPos(23.13, 113.26)) : ISetti
     override fun setWorkedGridQsos(qsos: Map<String, List<GridQso>>) = TODO()
     override fun getRoamedGrids(): Set<String> = TODO()
     override fun setRoamedGrids(grids: Set<String>) = TODO()
-    override fun getMarkedGridStations(): Map<String, com.rtbishop.look4sat.core.domain.model.MarkedStation> = emptyMap()
-    override fun setMarkedGridStations(stations: Map<String, com.rtbishop.look4sat.core.domain.model.MarkedStation>) = Unit
+    override fun getMarkedGridStations(): Map<String, List<com.rtbishop.look4sat.core.domain.model.MarkedStation>> = emptyMap()
+    override fun setMarkedGridStations(stations: Map<String, List<com.rtbishop.look4sat.core.domain.model.MarkedStation>>) = Unit
     override fun updateLoTWSettings(settings: LoTWSettings) = TODO()
     override fun getLastLotwSyncDate(): String = ""
     override fun setLastLotwSyncDate(date: String) = Unit