fix(net): honor retail graceful logout handshake

Send the active character id, drain until the authoritative server confirmation, then emit retail's zero-sequence connection disconnect with the negotiated receiver iteration. The connected gate now waits for ACE to remove the exact UDP session before reconnecting, eliminating fixed-delay races.

tests/AcDream.Core.Net.Tests/Messages/CharacterLogOffTests.cs

@@ -0,0 +1,36 @@
+using System.Buffers.Binary;
+using AcDream.Core.Net.Messages;
+
+namespace AcDream.Core.Net.Tests.Messages;
+
+public sealed class CharacterLogOffTests
+{
+    [Fact]
+    public void BuildRequestBody_MatchesRetailOpcodeThenCharacterId()
+    {
+        byte[] body = CharacterLogOff.BuildRequestBody(0x5000000Au);
+
+        Assert.Equal(8, body.Length);
+        Assert.Equal(
+            CharacterLogOff.Opcode,
+            BinaryPrimitives.ReadUInt32LittleEndian(body));
+        Assert.Equal(
+            0x5000000Au,
+            BinaryPrimitives.ReadUInt32LittleEndian(body.AsSpan(4)));
+    }
+
+    [Fact]
+    public void IsConfirmation_AcceptsServerOpcodeOnlyBody()
+    {
+        byte[] body = BitConverter.GetBytes(CharacterLogOff.Opcode);
+
+        Assert.True(CharacterLogOff.IsConfirmation(body));
+    }
+
+    [Fact]
+    public void IsConfirmation_RejectsTruncatedOrDifferentMessage()
+    {
+        Assert.False(CharacterLogOff.IsConfirmation([0x53, 0xF6, 0x00]));
+        Assert.False(CharacterLogOff.IsConfirmation(BitConverter.GetBytes(0xF654u)));
+    }
+}