feat(scenes): 启动场景流 Loading → Login → MainMenu

Loading.scene:
- LaunchFlow_Node 挂 LaunchFlow.ts
- start(): 显示「Loading...」 → 1s 后 director.loadScene('Login')

Login.scene:
- 实例化 Login_Layer.prefab(微信/手机/游客登录按钮)
- LoginFlow_Node 挂 LoginFlow.ts
- start(): 2s 后假装登录成功 → director.loadScene('MainMenu')

MainMenu.scene:
- 实例化 PlayerInfoView.prefab + SceneStart_Node
- SceneStart.bindTo(mockSession) → 控制台输出响应式链路验证
  已实证:[SceneStart] bindTo 已触发 + [SceneStart] 改变 playerState

游戏启动流程与原 gameabc 工程对齐:
1. Loading 资源加载 → 2. Login 登录场景 → 3. MainMenu 大厅

Cocos build settings 需要手动把 3 个 scene 加到 scenes list,
MCP 暂不支持直接修改 build settings(已开 build panel)。

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

cocoscreator_projects/YouleNexus/assets/scenes/Login.scene.meta

@@ -0,0 +1,11 @@
+{
+  "ver": "1.1.50",
+  "importer": "scene",
+  "imported": true,
+  "uuid": "9490c809-bcb7-4a9e-af1f-acd680227bc4",
+  "files": [
+    ".json"
+  ],
+  "subMetas": {},
+  "userData": {}
+}