feat: stats — per-band mode split (CW / phone / data) stacked bar chart

Adds Stats.ByBandCategory (per band: CW/phone/data counts, band-plan order) via a
modeCategory() bucketing in stats.go, and a StackedBandBars chart in the Stats
panel showing the split per band with a legend.

frontend/wailsjs/go/models.ts

@@ -3411,6 +3411,26 @@ export namespace qslcard {
 
 export namespace qso {
 	
+	export class BandCategory {
+	    band: string;
+	    cw: number;
+	    phone: number;
+	    data: number;
+	    total: number;
+	
+	    static createFrom(source: any = {}) {
+	        return new BandCategory(source);
+	    }
+	
+	    constructor(source: any = {}) {
+	        if ('string' === typeof source) source = JSON.parse(source);
+	        this.band = source["band"];
+	        this.cw = source["cw"];
+	        this.phone = source["phone"];
+	        this.data = source["data"];
+	        this.total = source["total"];
+	    }
+	}
 	export class BandMode {
 	    band: string;
 	    mode: string;
@@ -3900,6 +3920,7 @@ export namespace qso {
 	    confirmed_any: number;
 	    by_mode: Bucket[];
 	    by_band: Bucket[];
+	    by_band_category: BandCategory[];
 	    by_operator: Bucket[];
 	    by_station: Bucket[];
 	    by_continent: Bucket[];
@@ -3939,6 +3960,7 @@ export namespace qso {
 	        this.confirmed_any = source["confirmed_any"];
 	        this.by_mode = this.convertValues(source["by_mode"], Bucket);
 	        this.by_band = this.convertValues(source["by_band"], Bucket);
+	        this.by_band_category = this.convertValues(source["by_band_category"], BandCategory);
 	        this.by_operator = this.convertValues(source["by_operator"], Bucket);
 	        this.by_station = this.convertValues(source["by_station"], Bucket);
 	        this.by_continent = this.convertValues(source["by_continent"], Bucket);