feat(auth): add Dev-only always-valid ISteamServer for local no-Steam clients

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

SVSim.UnitTests/Services/DevAlwaysValidSteamServerTests.cs

@@ -0,0 +1,25 @@
+using Microsoft.Extensions.Logging.Abstractions;
+using NUnit.Framework;
+using SVSim.EmulatedEntrypoint.Services;
+
+namespace SVSim.UnitTests.Services;
+
+[TestFixture]
+public class DevAlwaysValidSteamServerTests
+{
+    [Test]
+    public void BeginAuthSession_accepts_any_ticket_for_any_steamId()
+    {
+        var sut = new DevAlwaysValidSteamServer(NullLogger<DevAlwaysValidSteamServer>.Instance);
+
+        Assert.That(sut.BeginAuthSession(new byte[] { 0xDE, 0xAD }, 900001UL), Is.True);
+        Assert.That(sut.BeginAuthSession(System.Array.Empty<byte>(), 0UL), Is.True);
+    }
+
+    [Test]
+    public void Lifecycle_methods_do_not_throw()
+    {
+        var sut = new DevAlwaysValidSteamServer(NullLogger<DevAlwaysValidSteamServer>.Instance);
+        Assert.DoesNotThrow(() => { sut.Initialize(453480); sut.EndSession(900001UL); sut.Shutdown(); });
+    }
+}