Add server-side ELO ratings

scripts/ui/main.gd

@@ -131,6 +131,7 @@ func _build_ui() -> void:
 	screens["profile"] = profile
 
 	ProfileService.profile_changed.connect(_refresh_header_stats)
+	QuestionBankService.ratings_changed.connect(_refresh_header_stats)
 	AuthState.auth_changed.connect(_refresh_header_stats)
 	_refresh_header_stats()
 	_build_app_menu()
@@ -148,9 +149,8 @@ func _refresh_header_stats() -> void:
 	if header_stats == null:
 		return
 	var profile := ProfileService.get_profile()
-	header_stats.text = "LV %d  |  %d XP  |  Streak %d" % [
-		profile.get("level", 1),
-		profile.get("xp", 0),
+	header_stats.text = "ELO %d  |  Streak %d" % [
+		QuestionBankService.overall_elo,
 		profile.get("current_streak", 0)
 	]
 	if user_label != null: