test(client): cookies + middleware-based user injection for POSTs

- WebApplicationFactoryClientOptions.HandleCookies = true so the
  antiforgery cookie set on the GET that fetches the form is replayed
  on the POST that submits it. Without it, the antiforgery token is
  valid on the client but the server can't validate it, leading to
  400 BadRequest.
- Inject a middleware in TestWebApplicationFactory that promotes the
  X-Test-Role header to an authenticated ClaimsPrincipal on
  HttpContext.User, so anything that reads User.GetUserId() (or any
  other claim-based helper) downstream sees a logged-in identity.
  The TestAuthPolicyProvider only short-circuits [Authorize(...)]
  checks; it does not touch HttpContext.User, which is what user
  code reads.
- Fix the AddRedirectUri_POST test URL: it was posting to
  /Client/AddRedirectUri (no id) which 404'd; the action signature
  is (int id, string redirectUri) and the default route binds the id
  from the URL segment.

WIP: the MapStaticAssets() default lookup at
{AssemblyName}.staticwebassets.endpoints.json still needs the
manifest to be renamed on copy — the Yavsc.Org.Tests.csproj target
that does that is in this commit but the MSBuild string transform
has rough edges that prevent the rename from landing. Will revisit.

src/Yavsc.Org.Tests/TestWebApplicationFactory.cs

@@ -1,8 +1,11 @@
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc.Testing;
 using Microsoft.AspNetCore.TestHost;
 using Microsoft.Extensions.DependencyInjection;
+using System.Security.Claims;
+using System.Threading.Tasks;
 
 namespace Yavsc.Org.Tests;
 
@@ -16,6 +19,10 @@ namespace Yavsc.Org.Tests;
 /// <c>[Authorize("AdministratorOnly")]</c> (and any other policy
 /// requiring a role) is satisfied by sending an
 /// <c>X-Test-Role: Administrator</c> header, without a real login.
+/// Also injects a middleware that promotes the same header into a
+/// real <see cref="ClaimsPrincipal"/> on <c>HttpContext.User</c> so
+/// that user code reading <c>User.GetUserId()</c> sees a logged-in
+/// identity.
 /// </summary>
 public class TestWebApplicationFactory : WebApplicationFactory<Program>
 {
@@ -33,5 +40,38 @@ public class TestWebApplicationFactory : WebApplicationFactory<Program>
             // becomes irrelevant: any GetPolicyAsync call is routed here.
             services.AddSingleton<IAuthorizationPolicyProvider, TestAuthPolicyProvider>();
         });
+
+        // Promote the X-Test-Role header to an authenticated identity
+        // on the request, so anything that reads User.GetUserId() (or
+        // any other claim-based helper) downstream sees a logged-in
+        // user. The policy provider above only short-circuits
+        // [Authorize(...)] checks; it does not touch HttpContext.User.
+        builder.Configure(app =>
+        {
+            app.Use(InjectTestUser);
+        });
+    }
+
+    private static RequestDelegate InjectTestUser(RequestDelegate next)
+    {
+        return async ctx =>
+        {
+            var role = ctx.Request.Headers[TestAuthPolicyProvider.HeaderName].ToString();
+            if (!string.IsNullOrEmpty(role) &&
+                (ctx.User.Identity is null || !ctx.User.Identity.IsAuthenticated))
+            {
+                var identity = new ClaimsIdentity(
+                    new[]
+                    {
+                        new Claim(
+                            "http://schemas.microsoft.com/ws/2008/06/identity/claims/role",
+                            role),
+                        new Claim(ClaimTypes.NameIdentifier, "test-user"),
+                    },
+                    authenticationType: "TestAuth");
+                ctx.User = new ClaimsPrincipal(identity);
+            }
+            await next(ctx);
+        };
     }
 }