feat(S02/T01): Added CoverArtGroupURL for release-group cover art, conc…

- backend/explore/coverart.go
- backend/explore/explore.go
- backend/explore/coverart_test.go
- frontend/wailsjs/go/explore/Service.js
- frontend/wailsjs/go/explore/Service.d.ts

backend/explore/coverart.go

@@ -2,7 +2,10 @@ package explore
 
 import "fmt"
 
-const coverArtBaseURL = "https://coverartarchive.org/release"
+const (
+	coverArtBaseURL      = "https://coverartarchive.org/release"
+	coverArtGroupBaseURL = "https://coverartarchive.org/release-group"
+)
 
 // CoverArtURL returns the Cover Art Archive URL for the 250px
 // front cover of the given release MBID.
@@ -16,3 +19,18 @@ func CoverArtURL(releaseMBID string) string {
 func CoverArtURLSize(releaseMBID string, size int) string {
 	return fmt.Sprintf("%s/%s/front-%d", coverArtBaseURL, releaseMBID, size)
 }
+
+// CoverArtGroupURL returns the Cover Art Archive URL for the 250px
+// front cover of the given release group MBID.  Search results
+// return release group MBIDs (not release MBIDs), so this is the
+// correct endpoint for displaying cover art in search results.
+func CoverArtGroupURL(releaseGroupMBID string) string {
+	return fmt.Sprintf("%s/%s/front-250", coverArtGroupBaseURL, releaseGroupMBID)
+}
+
+// CoverArtGroupURLSize returns the Cover Art Archive URL for the
+// front cover of the given release group MBID at the specified
+// pixel size.  Common sizes are 250, 500, and 1200.
+func CoverArtGroupURLSize(releaseGroupMBID string, size int) string {
+	return fmt.Sprintf("%s/%s/front-%d", coverArtGroupBaseURL, releaseGroupMBID, size)
+}