feat(map): first-call callsign label toggle in VUCC grid mode

Add a 'first call' pill toggle below the grid-mode switch (map top-right,
visible only in grid mode + VUCC award). When on, worked (green) cells are
labelled with the first callsign worked in that grid (earliest confirmed
QSO by time) instead of the Maidenhead code; non-worked cells get no label
at all. Persisted via OtherSettings.stateOfMapFirstCall (full MVI chain).
The feature is VUCC-only: All and other award overlays never draw it.

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/model/Settings.kt

@@ -60,6 +60,10 @@ data class OtherSettings(
     val stateOfLightTheme: Boolean,
     val stateOfNightMode: Boolean = false,
     val stateOfMapGrid: Boolean = false,
+    /** Grid mode: label worked (green) cells with the FIRST callsign worked
+     *  in that grid instead of the Maidenhead code; non-worked cells get no
+     *  label at all. */
+    val stateOfMapFirstCall: Boolean = false,
     val shouldSeeWarning: Boolean,
     val shouldSeeWhatsNew: Boolean,
     val sstvMode: String = "Auto",