feat: show total LB play count on artist detail page

Added GetArtistPlayCount(mbid) — fetches ArtistPopularity from LB
for a single MBID and returns the total listen count. Fire-and-forget
call on the artist page, displays below the meta line as
'1.3M plays on ListenBrainz' (uses existing formatListenCount).

frontend/wailsjs/go/explore/Service.d.ts

@@ -19,6 +19,8 @@ export function GetArtistImages(arg1:Array<string>):Promise<Record<string, strin
 
 export function GetArtistMBID(arg1:string):Promise<string>;
 
+export function GetArtistPlayCount(arg1:string):Promise<number>;
+
 export function GetThumbnail(arg1:string,arg2:string,arg3:string):Promise<string>;
 
 export function GetThumbnails(arg1:Array<explore.ThumbnailRequest>):Promise<Record<string, string>>;

frontend/wailsjs/go/explore/Service.js

@@ -34,6 +34,10 @@ export function GetArtistMBID(arg1) {
   return window['go']['explore']['Service']['GetArtistMBID'](arg1);
 }
 
+export function GetArtistPlayCount(arg1) {
+  return window['go']['explore']['Service']['GetArtistPlayCount'](arg1);
+}
+
 export function GetThumbnail(arg1, arg2, arg3) {
   return window['go']['explore']['Service']['GetThumbnail'](arg1, arg2, arg3);
 }