chore: add QQ group to README, drop unused bootstrapForDll

- README: announce QQ group 523522206 for project discussion.
- ZenClient: remove bootstrapForDll(). The DLL path went from
  "GameLoaderBridge -> DllBootstrap.start -> new ZenClient" to just
  "DllBootstrap.start -> registerPatches + installPatchesAndRetransform"
  a few commits ago, so MinecraftPatch.onTick's existing lazy-init
  now constructs the singleton on the next tick and no external
  caller needs this helper anymore.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

README.md

@@ -1,5 +1,7 @@
 # Open Zen [WIP]
 
+> 欢迎加群 523522206 讨论该项目。
+
 > 截止至目前，Open Zen仍然处于早期构建阶段。大量特性可能仍不可用，请谅解！当您发现有不可用的功能，欢迎开Issues描述或直接提交Pull Request，我们将不胜感激！
 
 **Open Zen** 是 *Zen* Minecraft 客户端的反混淆源码版本，几乎是由 [Claude](https://claude.com/)协助逆向得到。目标版本为 **Minecraft 1.20.1 + Forge 47.4.20**。

src/main/java/shit/zen/ZenClient.java

@@ -79,18 +79,6 @@ public class ZenClient extends ClientBase {
         }
     }
 
-    /**
-     * Explicit entry point used by the DLL injection path
-     * ({@code shit.zen.dll.DllBootstrap}). Constructs the singleton if not
-     * already present and returns it.
-     */
-    public static synchronized ZenClient bootstrapForDll() {
-        if (instance == null) {
-            new ZenClient();
-        }
-        return instance;
-    }
-
     private void init() {
         try {
             username = System.getProperty("user.name", "Player");