feat(entry/stats/awards): Alt+W clear, slot drill-down, DXCC prefix column

Five operator-requested items:

- Alt+W clears the QSO entry. Handled before the `typing` guard and above
  the keyer's key routing, so there is always one key that clears whatever
  else is running — Esc is not that key when the CW keyer reserves it.

- The Grid box no longer pops outside the entry panel on a narrow window.
  Row 2 needed 300+130+76+gaps = 538 px inside a panel whose min-width is
  520, so Grid was pushed out and clipped at every narrow width, not just
  extreme ones. QTH's min-width drops to 80 and the row wraps rather than
  overflowing if it ever still can't fit.

- Selecting a QSO in the log now drives the Stats (F1) matrix. Uses its own
  WorkedBefore call into separate state, NOT runWorkedBefore: that one owns
  the entry form's wbRef and can trigger a field backfill, which browsing
  the log must never do. The entry form wins whenever it holds a call.

- Clicking a coloured band/mode square lists the contacts behind it. Returns
  the exact callsign AND the rest of the entity, because that pair is what
  the cell's colour encodes; the call's own QSOs are bolded. The DXCC arm
  matches the stored dxcc column only — reconstructing it from the callsign
  here would disagree with the matrix above, which is built from that column.

- The Awards DXCC list shows each entity's primary prefix in its own sortable
  column. Derived live from cty.dat into Ref.Group rather than stored on the
  reference row, so an existing installation needs no re-seed.

frontend/wailsjs/go/main/App.d.ts

@@ -87,6 +87,8 @@ export function AwardsFolder():Promise<string>;
 
 export function BackfillUSCounties():Promise<main.BackfillUSCountiesResult>;
 
+export function BandSlotQSOs(arg1:string,arg2:number,arg3:string,arg4:string):Promise<Array<qso.QSO>>;
+
 export function BrowseExecutable():Promise<string>;
 
 export function BulkUpdateField(arg1:Array<number>,arg2:string,arg3:string):Promise<number>;

frontend/wailsjs/go/main/App.js

@@ -122,6 +122,10 @@ export function BackfillUSCounties() {
   return window['go']['main']['App']['BackfillUSCounties']();
 }
 
+export function BandSlotQSOs(arg1, arg2, arg3, arg4) {
+  return window['go']['main']['App']['BandSlotQSOs'](arg1, arg2, arg3, arg4);
+}
+
 export function BrowseExecutable() {
   return window['go']['main']['App']['BrowseExecutable']();
 }