feat(onboarding): welcome eligible new players

src/main/java/games/dmg/leaf/LeafRuntime.java

@@ -2,6 +2,7 @@ package games.dmg.leaf;
 
 import java.io.IOException;
 import java.time.Instant;
+import java.time.temporal.ChronoUnit;
 import java.util.Objects;
 import java.util.UUID;
 import org.bukkit.Server;
@@ -51,6 +52,11 @@ public final class LeafRuntime {
         );
         stateManager.saveIfDirty();
         reconcile(player);
+        LeafSettings settings = settingsProvider.current();
+        Instant onboardingEnd = state.firstJoin().plus(settings.onboardingDays(), ChronoUnit.DAYS);
+        if (settings.enabled() && observedAt.isBefore(onboardingEnd)) {
+            player.sendMessage(LeafText.color(settings.welcomeMessage()));
+        }
         return state;
     }