compat: switch expression → ternary for .NET 4.8 双兼容

IsmctsBot.cs:539: C#8 switch expression → C#7.3 ternary
  num switch {1=>14,2=>16,_=>num} → num==1?14:num==2?16:num

bot代码(.NET 4.8)兼容性清单:
  ✅ LINQ (GroupBy/OrderBy/SelectMany) — 原生
  ✅ string 插值 $"..." — C#6
  ✅ ?./?? — C#6
  ✅ ValueTuple — 需 NuGet System.ValueTuple (net48)
  ✅ 已移除 switch expression — 唯一 C#8 特性

net48 项目集成只需3步:
  1. 复制 PdkBot.cs + IsmctsBot.cs → PdkFriendServer/Logic/
  2. csproj: <PackageReference Include="System.ValueTuple" Version="4.5.0"/>
  3. WaitWanJiaShuRu 加入 BotMode 分支(同 net10.0 逻辑)

PdkFriendServer/Logic/IsmctsBot.cs

@@ -536,7 +536,7 @@ namespace PdkFriendServer.Logic
             foreach (int flower in new[] { 1, 2, 3, 4 })
                 for (int num = 1; num <= 13; num++)
                 {
-                    int gameNum = num switch { 1 => 14, 2 => 16, _ => num };
+                    int gameNum = num == 1 ? (byte)14 : num == 2 ? (byte)16 : (byte)num;
                     deck.Add(new TCardInfoPdkF
                     {
                         ID = (byte)id++, Flower = (byte)flower,