Adds a partially usable arena menu openable through a command

src/main/java/net/knarcraft/minigames/command/MenuCommand.java

@@ -0,0 +1,46 @@
+package net.knarcraft.minigames.command;
+
+import net.knarcraft.minigames.MiniGames;
+import net.knarcraft.minigames.arena.ArenaSession;
+import net.knarcraft.minigames.config.Message;
+import org.bukkit.command.Command;
+import org.bukkit.command.CommandSender;
+import org.bukkit.command.TabExecutor;
+import org.bukkit.entity.Player;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * The command for opening up an arena's menu
+ */
+public class MenuCommand implements TabExecutor {
+
+    @Override
+    public boolean onCommand(@NotNull CommandSender commandSender, @NotNull Command command, @NotNull String s,
+                             @NotNull String[] arguments) {
+        if (!(commandSender instanceof Player player)) {
+            commandSender.sendMessage(Message.ERROR_PLAYER_ONLY.getMessage());
+            return false;
+        }
+
+        ArenaSession existingSession = MiniGames.getInstance().getSession(player.getUniqueId());
+        if (existingSession == null) {
+            commandSender.sendMessage(Message.ERROR_NOT_IN_ARENA.getMessage());
+            return false;
+        }
+
+        existingSession.getGUI().openFor(player);
+        return true;
+    }
+
+    @Nullable
+    @Override
+    public List<String> onTabComplete(@NotNull CommandSender commandSender, @NotNull Command command, @NotNull String s,
+                                      @NotNull String[] strings) {
+        return new ArrayList<>();
+    }
+
+}