feat(net+chat): #19 TurbineChat (0xF7DE) codec + ChatChannelInfo + SetTurbineChatChannels parser

Full port of holtburger's TurbineChat sidecar wire path:

- TurbineChat.cs: 0xF7DE codec with three payload variants
  (EventSendToRoom S->C, RequestSendToRoomById C->S, Response).
  10-field outer header (size_first/blob_type/dispatch_type/
  target_type/target_id/transport_type/transport_id/cookie/
  size_second + payload).
- UTF-16LE turbine string codec with 1-or-2 byte variable-length
  prefix (high bit on first byte signals 2-byte form). Mirrors
  holtburger's read_turbine_string / write_turbine_string at
  references/holtburger/.../messages/chat/turbine.rs:502-544.
- SetTurbineChatChannels.cs: 0x0295 GameEvent sub-opcode parser
  (10 x u32 channel ids). Wired through GameEventDispatcher in
  WorldSession ctor; routes to GameEventWiring + TurbineChatState.
- ChatChannelInfo.cs (Core): unified record union with Legacy
  (channel id + name) and Turbine (room id + chat type +
  dispatch type + name) variants, plus IsSelfEchoChannel
  predicate (Tells = false, channels = true so optimistic echo
  is suppressed where the server will echo).
- TurbineChatState.cs (Core): Enabled flag + 10 cached room ids
  + NextContextId() cookie counter starting at 1.
- WorldSession adds TurbineChatReceived + TurbineChannelsReceived
  events; SendTurbineChatTo outbound builds RequestSendToRoomById
  + sends through SendGameAction. ProcessDatagram dispatches
  0xF7DE at the top level.
- GameWindow constructs TurbineChatState, subscribes inbound
  EventSendToRoom -> ChatLog.OnChannelBroadcast; extends I.3's
  SendChatCmd handler to route Turbine kinds (General/Trade/Lfg/
  Roleplay/Society/Olthoi) through TurbineChat first, fall back
  to legacy ChatChannel send when state.Enabled == false.

Round-trip golden fixtures from holtburger source verified for
all three payload variants + UTF-16LE strings (short + long
prefix + non-ASCII Cafe + empty) + SetTurbineChatChannels.

26 new tests:
- TurbineChatTests, SetTurbineChatChannelsTests in Core.Net.Tests
- ChatChannelInfoTests, TurbineChatStateTests in Core.Tests

Solution total: 960 green (243 Core.Net + 625 Core + 92 UI).

ACE doesn't run a TurbineChat server, so codec is "ready when
needed" for retail-server-emulating setups. Legacy ChatChannel
fallback continues to work for current ACE-against-acdream play.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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

@@ -0,0 +1,96 @@
+using System;
+using AcDream.Core.Net.Messages;
+using Xunit;
+
+namespace AcDream.Core.Net.Tests.Messages;
+
+/// <summary>
+/// Phase I.6: <see cref="SetTurbineChatChannels"/> 10-u32 GameEvent
+/// payload parser.
+///
+/// <para>
+/// Golden fixture taken from holtburger
+/// <c>references/holtburger/crates/holtburger-protocol/src/messages/chat/turbine.rs</c>
+/// lines 654-679 (test <c>set_turbine_chat_channels_fixture</c>) — itself
+/// generated by ACE's <c>SyntheticProtocolTests.GenerateTurbineChatFixtures</c>.
+/// </para>
+/// </summary>
+public sealed class SetTurbineChatChannelsTests
+{
+    [Fact]
+    public void TryParse_HoltburgerGoldenFixture_RoundTrips()
+    {
+        // Full game-message body from turbine.rs:655-657:
+        //   B0F70000  – outer 0xF7B0 GameEvent opcode
+        //   00000000  – guid 0
+        //   21000000  – sequence 0x21
+        //   95020000  – eventType 0x0295 (SetTurbineChatChannels)
+        //   <40-byte payload>
+        byte[] full = HexDecode(
+            "B0F7000000000000210000009502000078563412" +
+            "020000000300000004000000050000000A000000" +
+            "09000000070000000800000009000000");
+
+        // The parser consumes only the 40-byte payload after the
+        // GameEventEnvelope header (16 bytes).
+        var env = GameEventEnvelope.TryParse(full);
+        Assert.NotNull(env);
+        Assert.Equal(GameEventType.SetTurbineChatChannels, env!.Value.EventType);
+
+        var parsed = SetTurbineChatChannels.TryParse(env.Value.Payload.Span);
+        Assert.NotNull(parsed);
+        // Allegiance: 0x12345678 (Unknown id used in fixture).
+        Assert.Equal(0x12345678u, parsed!.Value.AllegianceRoom);
+        // General..Olthoi
+        Assert.Equal(2u, parsed.Value.GeneralRoom);
+        Assert.Equal(3u, parsed.Value.TradeRoom);
+        Assert.Equal(4u, parsed.Value.LfgRoom);
+        Assert.Equal(5u, parsed.Value.RoleplayRoom);
+        Assert.Equal(10u, parsed.Value.OlthoiRoom);
+        // Society = SocietyRadiantBlood (id 9) per fixture
+        Assert.Equal(9u, parsed.Value.SocietyRoom);
+        // Sub-society rooms 7, 8, 9
+        Assert.Equal(7u, parsed.Value.SocietyCelestialHandRoom);
+        Assert.Equal(8u, parsed.Value.SocietyEldrytchWebRoom);
+        Assert.Equal(9u, parsed.Value.SocietyRadiantBloodRoom);
+    }
+
+    [Fact]
+    public void Serialize_RoundTripsThroughTryParse()
+    {
+        var original = new SetTurbineChatChannels.Parsed(
+            AllegianceRoom: 0x100,
+            GeneralRoom: 0x200,
+            TradeRoom: 0x300,
+            LfgRoom: 0x400,
+            RoleplayRoom: 0x500,
+            OlthoiRoom: 0x600,
+            SocietyRoom: 0x700,
+            SocietyCelestialHandRoom: 0x800,
+            SocietyEldrytchWebRoom: 0x900,
+            SocietyRadiantBloodRoom: 0xA00);
+
+        byte[] payload = SetTurbineChatChannels.Serialize(original);
+        Assert.Equal(SetTurbineChatChannels.PayloadSize, payload.Length);
+
+        var roundTripped = SetTurbineChatChannels.TryParse(payload);
+        Assert.NotNull(roundTripped);
+        Assert.Equal(original, roundTripped!.Value);
+    }
+
+    [Fact]
+    public void TryParse_TruncatedPayload_ReturnsNull()
+    {
+        // 39 bytes — one short of the 40-byte minimum.
+        Assert.Null(SetTurbineChatChannels.TryParse(new byte[39]));
+    }
+
+    private static byte[] HexDecode(string hex)
+    {
+        if ((hex.Length & 1) != 0) throw new ArgumentException("hex length must be even");
+        byte[] result = new byte[hex.Length / 2];
+        for (int i = 0; i < result.Length; i++)
+            result[i] = Convert.ToByte(hex.Substring(i * 2, 2), 16);
+        return result;
+    }
+}