Add configurable particle slot model

Introduce parameters, particle types, designs and entries that build the
existing particle elements, store each of the 7 particle slots in its own
UserConfig key, and let LobbyPlayer select a slot next to the old enum
particles. Slots 4-5 need a team, 6-7 the server team.

LobbySystem/src/de/steamwar/lobby/particle/design/DesignVisibility.java

@@ -0,0 +1,29 @@
+/*
+ *   This file is a part of the SteamWar software.
+ *
+ *   Copyright (C) 2026 SteamWar.de-Serverteam
+ *
+ *   This program is free software: you can redistribute it and/or modify
+ *   it under the terms of the GNU Affero General Public License as published by
+ *   the Free Software Foundation, either version 3 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ *   GNU Affero General Public License for more details.
+ *
+ *   You should have received a copy of the GNU Affero General Public License
+ *   along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package de.steamwar.lobby.particle.design;
+
+public enum DesignVisibility {
+    // Offered in the builder to everyone
+    BASIC,
+    // Offered in the builder, usable once its requirement is met
+    REWARD,
+    // Only used by presets, never offered in the builder or accepted from storage
+    INTERNAL,
+}