feat: record who created join codes and who added each node [CI]

backend/tests/MoShiro.Backend.Tests/InstallTests.cs

@@ -56,6 +56,13 @@ public sealed class InstallTests
         Assert.DoesNotContain("@@", powershell, StringComparison.Ordinal);
     }
 
+    [Fact]
+    public async Task Codes_RecordWhoCreatedThem()
+    {
+        JsonNode created = await CreateAsync("agent");
+        Assert.StartsWith("key:", created["token"]!["created_by"]!.GetValue<string>(), StringComparison.Ordinal); // Admin 客户端是 API key
+    }
+
     [Fact]
     public async Task Script_IsNotServedForUnknownRevokedOrUsedUpCodes()
     {