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

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

@@ -106,10 +106,10 @@ interface ISettingsRepo {
     fun getRoamedGrids(): Set<String>
     fun setRoamedGrids(grids: Set<String>)
     /** Stations the user marked as "want to contact" in unworked gridsquares
-     *  (grid -> mark). One mark per grid; cleared automatically when the grid
-     *  becomes worked. */
-    fun getMarkedGridStations(): Map<String, com.rtbishop.look4sat.core.domain.model.MarkedStation>
-    fun setMarkedGridStations(stations: Map<String, com.rtbishop.look4sat.core.domain.model.MarkedStation>)
+     *  (grid -> ordered list of marks; the first is the pinned/top one). The
+     *  whole grid clears automatically once it becomes worked. */
+    fun getMarkedGridStations(): Map<String, List<com.rtbishop.look4sat.core.domain.model.MarkedStation>>
+    fun setMarkedGridStations(stations: Map<String, List<com.rtbishop.look4sat.core.domain.model.MarkedStation>>)
     //endregion
 
     //region # LoTW confirmed-grids settings

core/domain/src/test/java/com/rtbishop/look4sat/core/domain/repository/LoTWGridSyncTest.kt

@@ -262,9 +262,9 @@ class LoTWGridSyncTest {
         override fun setWorkedGridQsos(qsos: Map<String, List<GridQso>>) { workedGridQsos = qsos }
         override fun getRoamedGrids(): Set<String> = roamedGrids
         override fun setRoamedGrids(grids: Set<String>) { roamedGrids = grids }
-        private var markedGridStations: Map<String, MarkedStation> = emptyMap()
-        override fun getMarkedGridStations(): Map<String, MarkedStation> = markedGridStations
-        override fun setMarkedGridStations(stations: Map<String, MarkedStation>) { markedGridStations = stations }
+        private var markedGridStations: Map<String, List<MarkedStation>> = emptyMap()
+        override fun getMarkedGridStations(): Map<String, List<MarkedStation>> = markedGridStations
+        override fun setMarkedGridStations(stations: Map<String, List<MarkedStation>>) { markedGridStations = stations }
         override fun getLastLotwSyncDate(): String = lastSyncDate
         override fun setLastLotwSyncDate(date: String) { lastSyncDate = date }
         override fun getLastLotwSyncCallsign(): String = lastSyncCallsign