test(benchmarks): add C#/ASP.NET and TypeScript tasks

Six tasks with hidden checks: ASP.NET validation and 404 handling, C#
cancellation, and TypeScript overlap, deep merge, and debounce fixes, checked
with dotnet run and node --test.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/benchmarks/tasks/16-aspnet-unknown-customer/task.json

@@ -0,0 +1,13 @@
+{
+  "prompt": "Requesting an unknown customer with GET /customers/{id} returns HTTP 500. Return 404 instead, and keep known customers working.",
+  "check": [
+    "dotnet",
+    "run",
+    "--project",
+    "bench_hidden/Check",
+    "--nologo"
+  ],
+  "workflow": {
+    "kind": "C#/ASP.NET change"
+  }
+}