Add BackupKit and mid-game kit selection

Introduce a BackupKit and allow players holding it to change kits mid-game while preventing normal kits from being picked once the game started. Changes:
- Add BackupKit implementation (kit with no abilities/items used for mid-round kit selection).
- Update KitCommand: import BackupKit and GameState, add isIngame helper, disallow normal kit picks during INGAME/INVINCIBILITY, permit BackupKit to swap kits mid-game (but prevent picking the same kit) and apply playstyles accordingly.
- Fix GoblinKit to also copy/restore the target's playstyle when stealing a kit and restore the player's original playstyle after timeout.
- Tweak IceMageKit slow effect chance (now ~1/3 chance using random.nextInt(3) < 1).
- Update en_US.yml: add messages and kit strings for backup and icemage, adjust ability_charged color, and add game/cannot-pick messages.

Also includes small import and formatting adjustments.

src/main/kotlin/club/mcscrims/speedhg/command/KitCommand.kt

@@ -1,7 +1,9 @@
 package club.mcscrims.speedhg.command
 
 import club.mcscrims.speedhg.SpeedHG
+import club.mcscrims.speedhg.game.GameState
 import club.mcscrims.speedhg.kit.Playstyle
+import club.mcscrims.speedhg.kit.impl.BackupKit
 import club.mcscrims.speedhg.util.legacySerializer
 import club.mcscrims.speedhg.util.sendMsg
 import org.bukkit.command.Command
@@ -52,6 +54,30 @@ class KitCommand : CommandExecutor, TabCompleter {
 			return true
 		}
 
+		val playerKit = plugin.kitManager.getSelectedKit( player )
+		val isBackup = playerKit != null && playerKit is BackupKit
+
+		if ( !isBackup && isIngame() )
+		{
+			player.sendMsg("commands.kit.gameHasStarted")
+			return true
+		}
+		else if ( isBackup && isIngame() )
+		{
+			if ( kit is BackupKit )
+			{
+				player.sendMsg( "commands.kit.cannotPickSameKit" )
+				return true
+			}
+
+			plugin.kitManager.selectKit( player, kit )
+			plugin.kitManager.selectPlaystyle( player, playstyle )
+			plugin.kitManager.applyKit( player )
+
+			player.sendMsg( "commands.kit.selected", "playstyle" to playstyle.displayName, "kit" to legacySerializer.serialize( kit.displayName ))
+			return true
+		}
+
 		plugin.kitManager.selectKit( player, kit )
 		plugin.kitManager.selectPlaystyle( player, playstyle )
 
@@ -78,4 +104,10 @@ class KitCommand : CommandExecutor, TabCompleter {
 		return listOf()
 	}
 
+	private fun isIngame(): Boolean = when ( plugin.gameManager.currentState )
+	{
+		GameState.INGAME, GameState.INVINCIBILITY -> true
+		else                                      -> false
+	}
+
 }