feat(map): mark a station you want to contact in unworked grids

- New MarkedStation model + ISettingsRepo/SettingsRepo persistence
  (single JSON key markedGridStations, org.json only)
- MapState/MapViewModel: markedGrids state, Set/RemoveMarkedStation
  actions; marks auto-clear once the grid becomes worked
- MaidenheadGridOverlay: red fill (alpha 90, same as green worked
  fill) for marked grids at both zoom levels; first-call label mode
  shows the marked callsign in pale yellow on red cells
- MapScreen: unworked-grid dialog gains a 'mark a station you want
  to contact' button + callsign input dialog; marked row shows red
  callsign, 'Marked' in the count column, marking date, delete icon
- i18n: values/ + values-zh/ (grid_mark_*)

core/presentation/src/main/res/values-zh/strings.xml

@@ -131,6 +131,12 @@
     <string name="grid_qso_first">首通</string>
     <string name="grid_qso_no_sat">卫星未知</string>
     <string name="grid_qso_match">匹配</string>
+    <!-- 未通联网格中的“标记想通联的电台”提醒 -->
+    <string name="grid_mark_station">标记你想通联的电台</string>
+    <string name="grid_mark_callsign">呼号</string>
+    <string name="grid_mark_confirm">标记</string>
+    <string name="grid_mark_label">标记</string>
+    <string name="grid_mark_delete">删除标记</string>
     <string name="map_visible">日照中</string>
 
     <!-- Settings screen -->

core/presentation/src/main/res/values/strings.xml

@@ -151,6 +151,12 @@
     <string name="grid_qso_first">First</string>
     <string name="grid_qso_no_sat">satellite unknown</string>
     <string name="grid_qso_match">Match</string>
+    <!-- Mark-a-station reminder in unworked grids -->
+    <string name="grid_mark_station">Mark a station you want to contact</string>
+    <string name="grid_mark_callsign">Callsign</string>
+    <string name="grid_mark_confirm">Mark</string>
+    <string name="grid_mark_label">Marked</string>
+    <string name="grid_mark_delete">Remove mark</string>
     <string name="map_visible">Visible</string>
 
     <!-- Settings screen -->