feat: top releases sorted by popularity with library-style album cards

Replaced the date-sorted release group approach with a dedicated
TopReleaseGroupsForArtist LB API call that returns releases ranked
by total listen count (popularity). Added LBTopReleaseGroup type
and Wails bindings.

Restyled the top-releases cards to match the library album view:
square cover art on top with title and type below, centered text,
auto-filling the available width with even spacing.

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

@@ -50,3 +50,5 @@ export function StartIndexBuild():Promise<void>;
 export function StopIndexBuild():Promise<void>;
 
 export function TopRecordingsForArtist(arg1:string):Promise<Array<explore.LBTopRecording>>;
+
+export function TopReleaseGroupsForArtist(arg1:string):Promise<Array<explore.LBTopReleaseGroup>>;

frontend/wailsjs/go/explore/Service.js

@@ -97,3 +97,7 @@ export function StopIndexBuild() {
 export function TopRecordingsForArtist(arg1) {
   return window['go']['explore']['Service']['TopRecordingsForArtist'](arg1);
 }
+
+export function TopReleaseGroupsForArtist(arg1) {
+  return window['go']['explore']['Service']['TopReleaseGroupsForArtist'](arg1);
+}

frontend/wailsjs/go/models.ts

@@ -34,6 +34,26 @@ export namespace explore {
 	        this.totalListenCount = source["totalListenCount"];
 	    }
 	}
+	export class LBTopReleaseGroup {
+	    releaseGroupMbid: string;
+	    title: string;
+	    artistName: string;
+	    type: string;
+	    totalListenCount: number;
+	
+	    static createFrom(source: any = {}) {
+	        return new LBTopReleaseGroup(source);
+	    }
+	
+	    constructor(source: any = {}) {
+	        if ('string' === typeof source) source = JSON.parse(source);
+	        this.releaseGroupMbid = source["releaseGroupMbid"];
+	        this.title = source["title"];
+	        this.artistName = source["artistName"];
+	        this.type = source["type"];
+	        this.totalListenCount = source["totalListenCount"];
+	    }
+	}
 	export class MBArtist {
 	    mbid: string;
 	    name: string;