feat(log): QSO number column, oldest contact = 1

Not the id: the primary key follows insertion order, so importing an old ADIF
gives the oldest contacts the highest ids. This is a rank over qso_date.

Computed over the WHOLE log, not the query result — ranking inside the result
would renumber every contact the moment a filter is applied, and QSO #1 would
change identity as the operator typed.

Held as one id-to-rank map, built from a single ordered id query and dropped
with the other derived indexes when the log changes. A contact logged from the
entry form is the newest, so it takes the next number without rereading the
log: AddQSO deliberately avoids full invalidation because a contest run would
pay for it once per QSO. A contact entered with an OLDER date belongs in the
middle of the order, so there the map is dropped and rebuilt rather than
mis-numbered.

frontend/src/components/RecentQSOsGrid.tsx

@@ -132,6 +132,10 @@ function qsoDistanceKm(d: any, myGrid?: string): number | undefined {
 
 export const makeColCatalog = (t: TFn, myGrid?: string): ColEntry[] => [
   // ── QSO basics ──
+  // Position in the log, oldest = 1. Filled by the backend over the WHOLE log,
+  // so it does not change when a filter narrows what is shown.
+  { group: 'QSO', label: t('rqg.c.number'), colId: 'number', headerName: t('rqg.h.number'), field: 'number' as any, width: 80, type: 'rightAligned', cellClass: 'font-mono',
+    comparator: (a, b) => (a ?? 0) - (b ?? 0) },
   { group: 'QSO', label: t('rqg.c.qso_date'),  colId: 'qso_date', headerName: t('rqg.c.qso_date'), field: 'qso_date' as any, width: 150, cellClass: 'font-mono', valueFormatter: (p) => fmtDateUTC(p.value), sort: 'desc', defaultVisible: true },
   { group: 'QSO', label: t('rqg.c.qso_date_off'),  colId: 'qso_date_off', headerName: t('rqg.c.qso_date_off'), field: 'qso_date_off' as any, width: 150, cellClass: 'font-mono', valueFormatter: (p) => fmtDateUTC(p.value) },
   { group: 'QSO', label: t('rqg.c.callsign'),  colId: 'callsign', headerName: t('rqg.c.callsign'), field: 'callsign' as any, width: 110, cellClass: 'font-mono font-semibold', defaultVisible: true },

frontend/wailsjs/go/models.ts

@@ -4206,6 +4206,7 @@ export namespace qso {
 	}
 	export class QSO {
 	    id: number;
+	    number?: number;
 	    callsign: string;
 	    // Go type: time
 	    qso_date: any;
@@ -4346,6 +4347,7 @@ export namespace qso {
 	    constructor(source: any = {}) {
 	        if ('string' === typeof source) source = JSON.parse(source);
 	        this.id = source["id"];
+	        this.number = source["number"];
 	        this.callsign = source["callsign"];
 	        this.qso_date = this.convertValues(source["qso_date"], null);
 	        this.qso_date_off = this.convertValues(source["qso_date_off"], null);