Allow audiusAppUrl to be overridden via env var

Add audiusAppUrl env var to Cfg initializer and guard the hardcoded
dev/prod defaults so an explicit env value is not clobbered by init().

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: rickyrombo

config/config.go

@@ -82,6 +82,7 @@ var Cfg = Config{
 	LaunchpadDeterministicSecret:          os.Getenv("launchpadDeterministicSecret"),
 	UnsplashKeys:                          strings.Split(os.Getenv("unsplashKeys"), ","),
 	AudiusApiSecret:                       os.Getenv("audiusApiSecret"),
+	AudiusAppUrl:                          os.Getenv("audiusAppUrl"),
 	NotificationCampaignOpenMetricsSecret: os.Getenv("notificationCampaignOpenMetricsSecret"),
 }
 
@@ -123,7 +124,9 @@ func init() {
 		Cfg.UploadNodes = DevUploadNodes
 		Cfg.AudiusdChainID = core_config.DevAcdcChainID
 		Cfg.AudiusdEntityManagerAddress = core_config.DevAcdcAddress
-		Cfg.AudiusAppUrl = "http://localhost:3000"
+		if Cfg.AudiusAppUrl == "" {
+			Cfg.AudiusAppUrl = "http://localhost:3000"
+		}
 	case "stage":
 		fallthrough
 	case "staging":
@@ -212,7 +215,9 @@ func init() {
 		Cfg.ChainId = "audius-mainnet-alpha-beta"
 		Cfg.AudiusdChainID = core_config.ProdAcdcChainID
 		Cfg.AudiusdEntityManagerAddress = core_config.ProdAcdcAddress
-		Cfg.AudiusAppUrl = "https://audius.co"
+		if Cfg.AudiusAppUrl == "" {
+			Cfg.AudiusAppUrl = "https://audius.co"
+		}
 		Cfg.RewardCodeAuthorizedKeys = []string{"4oGhuh6MkypUTnwUzKbtnUwFzjfaMWAgKYudchPfbYu8", "DDT15s6MMNxE4jkyGN46wNYqrgLWofT6WAvWtjYYrCUq"}
 		Cfg.VerifierAddress = "0xbeef8E42e8B5964fDD2b7ca8efA0d9aef38AA996"
 		Cfg.ArtistCoinRewardsStaticSenders = []Node{