[ads] Update in-process ads service startup delay to match Griffin

Adjust the in-process ads service startup delay to match Griffin’s, now
that a zero-delay rollout has been deployed across all build channels.
This change ensures consistent ad service initialization behavior across
platforms without requiring Griffin seed updates.

Author: tmancey

browser/brave_ads/services/bat_ads_service_factory_impl.cc

@@ -30,7 +30,7 @@ BASE_FEATURE(kInProcessBraveAdsServiceFeature,
              base::FEATURE_ENABLED_BY_DEFAULT);
 
 constexpr base::FeatureParam<base::TimeDelta> kBraveAdsServiceStartupDelay{
-    &kInProcessBraveAdsServiceFeature, "startup_delay", base::Seconds(3)};
+    &kInProcessBraveAdsServiceFeature, "startup_delay", base::Seconds(0)};
 
 // Binds the `receiver` to a new provider on a background task runner.
 void BindInProcessBatAdsService(