💥 feat(planning)!: 拆分 C# ICSP 并默认 Rust

* 新增可选 Flyshot.CSharp.Planning 项目

* 将 icsp 映射到 Rust 后端并拒绝旧 icsp_rust

* 补充后端注册、文档、调试页和回归测试

BREAKING CHANGE: method=icsp 现在默认调用 Rust 后端；C# ICSP 改为 method=icsp-csharp，旧 method=icsp_rust 不再作为正式入口。

tests/Flyshot.Core.Tests/OfflinePlanTests.cs

@@ -1,4 +1,5 @@
 using Flyshot.Core.Config;
+using Flyshot.CSharp.Planning;
 using Flyshot.Core.Domain;
 using Flyshot.Core.Planning;
 using Flyshot.Core.Planning.Export;
@@ -55,7 +56,7 @@ public sealed class OfflinePlanTests
         var request = new TrajectoryRequest(
             robot: scaledProfile,
             program: program,
-            method: useSelfAdapt ? PlanningMethod.SelfAdaptIcsp : PlanningMethod.Icsp);
+            method: useSelfAdapt ? PlanningMethod.SelfAdaptIcsp : PlanningMethod.IcspCSharp);
 
         PlannedTrajectory trajectory;
         if (useSelfAdapt)