Add server-side ELO ratings

scripts/ui/main_menu.gd

@@ -10,7 +10,7 @@ func _ready() -> void:
 	add_theme_constant_override("separation", 18)
 
 	var headline := Label.new()
-	headline.text = "Answer board-style questions. Earn XP. Unlock the map."
+	headline.text = "Answer board-style questions. Raise your ELO. Unlock the map."
 	headline.autowrap_mode = TextServer.AUTOWRAP_WORD_SMART
 	Style.set_label(headline, 38, Style.TEXT)
 	add_child(headline)
@@ -31,7 +31,7 @@ func _ready() -> void:
 	hero.add_child(hero_content)
 
 	var loop := Label.new()
-	loop.text = "XP Rush  |  Streak Heat  |  System Zones  |  Timed Blocks"
+	loop.text = "ELO Climb  |  Streak Heat  |  System Zones  |  Timed Blocks"
 	Style.set_label(loop, 24, Style.CYAN)
 	hero_content.add_child(loop)
 
@@ -72,9 +72,8 @@ func _ready() -> void:
 
 func on_show(_payload: Variant = null) -> void:
 	var profile := ProfileService.get_profile()
-	stats_label.text = "Level %d  |  %d XP  |  Current streak: %d  |  Badges: %d" % [
-		profile["level"],
-		profile["xp"],
+	stats_label.text = "ELO %d  |  Current streak: %d  |  Badges: %d" % [
+		QuestionBankService.overall_elo,
 		profile["current_streak"],
 		profile["badges"].size()
 	]