feat: Implement tile scarcity model for tile generation and power-up inventory UI for player interaction.

scripts/managers/player_input_manager.gd

@@ -89,14 +89,24 @@ func handle_unhandled_input(event):
 	# --- Keyboard Shortcuts (Event-based) ---
 	if event is InputEventKey and event.pressed and not event.echo:
 		match event.keycode:
-			KEY_KP_1, KEY_1:
-				player.activate_powerup(0) # FASTER_SPEED
-			KEY_KP_2, KEY_2:
-				player.activate_powerup(2) # BLOCK_FLOOR
-			KEY_KP_3, KEY_3:
-				player.activate_powerup(1) # AREA_FREEZE
-			KEY_KP_4, KEY_4:
-				player.activate_powerup(3) # INVISIBLE_MODE
+			KEY_KP_1, KEY_1, KEY_KP_2, KEY_2, KEY_KP_3, KEY_3, KEY_KP_4, KEY_4:
+				var is_sng = LobbyManager.game_mode == "Stop n Go"
+				match event.keycode:
+					KEY_KP_1, KEY_1:
+						player.activate_powerup(0) # FASTER_SPEED
+					KEY_KP_2, KEY_2:
+						if is_sng:
+							player.activate_powerup(1) # AREA_FREEZE (StopNGo)
+						else:
+							player.activate_powerup(2) # BLOCK_FLOOR (Free)
+					KEY_KP_3, KEY_3:
+						if is_sng:
+							player.activate_powerup(3) # INVISIBLE_MODE (StopNGo)
+						else:
+							player.activate_powerup(1) # AREA_FREEZE (Free)
+					KEY_KP_4, KEY_4:
+						if not is_sng:
+							player.activate_powerup(3) # INVISIBLE_MODE (Free)
 			# KEY_R:
 			# 	player.auto_put_item()
 			KEY_Q: