feat(vucc): per operated-grid VUCC counting

GridQso gains myGrid (ADIF MY_GRIDSQUARE) captured per QSO during LoTW
parsing (handles alphabetical field order + EOR reset) and persisted as
JSON key 'mg' (absent in pre-myGrid data -> null). Legacy syncs keep the
global VUCC count; one resync unlocks per-grid counting.

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

@@ -48,7 +48,9 @@ data class GridQso(
     val dxcc: Int? = null,
     val country: String? = null,
     val cqz: Int? = null,
-    val state: String? = null
+    val state: String? = null,
+    /** 4-char grid the station itself operated from (ADIF MY_GRIDSQUARE). */
+    val myGrid: String? = null
 ) {
     /** Short uplink/downlink band label ("U/V", "V/A"), or "" when unknown. */
     val bandLabel: String