Refactor Improve Purpur AFK system

* Move Leaf config init before Minecraft commands register
* Fix broken afk command cooldown
* Cleanup code

leaf-server/src/main/java/org/dreeam/leaf/config/modules/gameplay/AfkCommand.java

@@ -0,0 +1,23 @@
+package org.dreeam.leaf.config.modules.gameplay;
+
+import org.dreeam.leaf.config.ConfigModules;
+import org.dreeam.leaf.config.EnumConfigCategory;
+
+public class AfkCommand extends ConfigModules {
+
+    public String getBasePath() {
+        return EnumConfigCategory.GAMEPLAY.getBaseKeyName() + ".afk-command";
+    }
+
+    public static boolean enabled = false;
+
+    @Override
+    public void onLoaded() {
+        enabled = config.getBoolean(getBasePath() + ".enabled", enabled, config.pickStringRegionBased("""
+                The AFK command based on Minecraft built-in idle-timeout mechanism
+                Rest of AFK settings are in the Purpur config""",
+            """
+                基于原版 idle-timeout 系统的 AFK 指令
+                剩余配置项在 Purpur 配置里"""));
+    }
+}