feat: 项目初始化 + 3D方块世界原型 + AI助搭系统

初始化 monorepo: Go后端(7微服务) + Unity客户端(9模块) + 启动器

HTML5原型: Three.js 3D体素世界, Perlin噪声地形, 原版材质, 22种方块

Minecraft创造模式背包: 双栏布局, 拖拽移动物品, 方向性元件引脚

AI助搭策划文档 + 客户端/服务端骨架 + Docker Compose + CI

launcher/PCL-CE/PCL.Core/UI/Converters/NullToVisibilityConverter.cs

@@ -0,0 +1,22 @@
+using System;
+using System.Globalization;
+using System.Windows;
+using System.Windows.Data;
+
+namespace PCL.Core.UI.Converters;
+
+/// <summary>
+/// 将可 null 的值转换为 WPF Visibility 状态：若为 null 则折叠，否则可见
+/// </summary>
+public sealed class NullToVisibilityConverter : IValueConverter
+{
+    public object Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        return value is not null ? Visibility.Visible : Visibility.Collapsed;
+    }
+
+    public object ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
+    {
+        throw new NotSupportedException();
+    }
+}