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>

src/AcDream.Core/Chat/TurbineChatState.cs

@@ -0,0 +1,136 @@
+namespace AcDream.Core.Chat;
+
+/// <summary>
+/// Runtime state for retail's TurbineChat (0xF7DE) global chat rooms —
+/// the General / Trade / LFG / Roleplay / Society / Olthoi pipeline.
+///
+/// <para>
+/// Lifecycle:
+/// <list type="bullet">
+/// <item>Pre-login: <see cref="Enabled"/> false, all room ids 0, context counter 1.</item>
+/// <item>Server fires <c>SetTurbineChatChannels (0x0295)</c> shortly after EnterWorld
+///     → <see cref="OnChannelsReceived"/> populates the room ids and flips
+///     <see cref="Enabled"/> on.</item>
+/// <item>Outbound chat: caller asks for a fresh context id via
+///     <see cref="NextContextId"/>, looks up the room id by
+///     <see cref="ChatType"/>, and feeds the pair to
+///     <see cref="WorldSession.SendTurbineChatTo"/>.</item>
+/// </list>
+/// </para>
+///
+/// <para>
+/// Mirrors holtburger's <c>TurbineChatState</c>
+/// (<c>references/holtburger/crates/holtburger-core/src/client/types.rs</c>
+/// lines 657-672). Cookie counter starts at 1 (not 0) per holtburger:
+/// <c>next_context_id.wrapping_add(1).max(1)</c> keeps 0 reserved for
+/// "no context" / response cookies.
+/// </para>
+/// </summary>
+public sealed class TurbineChatState
+{
+    /// <summary>True after the first <c>SetTurbineChatChannels</c> arrives.</summary>
+    public bool Enabled { get; private set; }
+
+    /// <summary>Allegiance Turbine room (0 if player has no allegiance).</summary>
+    public uint AllegianceRoom { get; private set; }
+    public uint GeneralRoom { get; private set; }
+    public uint TradeRoom { get; private set; }
+    public uint LfgRoom { get; private set; }
+    public uint RoleplayRoom { get; private set; }
+    public uint OlthoiRoom { get; private set; }
+    /// <summary>Top-level Society room (0 if player has no society).</summary>
+    public uint SocietyRoom { get; private set; }
+    public uint SocietyCelestialHandRoom { get; private set; }
+    public uint SocietyEldrytchWebRoom { get; private set; }
+    public uint SocietyRadiantBloodRoom { get; private set; }
+
+    private uint _nextContextId = 1;
+
+    /// <summary>
+    /// Get-and-increment the per-session context cookie. Wraps to 1 (not
+    /// 0) so 0 stays reserved for "no context" / Response cookies.
+    /// Mirrors holtburger's <c>wrapping_add(1).max(1)</c>.
+    /// </summary>
+    public uint NextContextId()
+    {
+        uint cookie = _nextContextId;
+        unchecked
+        {
+            _nextContextId += 1;
+            if (_nextContextId == 0) _nextContextId = 1;
+        }
+        return cookie;
+    }
+
+    /// <summary>
+    /// Absorb a parsed <c>SetTurbineChatChannels</c> payload — flips
+    /// <see cref="Enabled"/> on and fills in the per-channel room ids.
+    /// Takes raw u32s (rather than the parser's struct directly) so
+    /// AcDream.Core stays free of an AcDream.Core.Net dependency.
+    /// </summary>
+    public void OnChannelsReceived(
+        uint allegianceRoom,
+        uint generalRoom,
+        uint tradeRoom,
+        uint lfgRoom,
+        uint roleplayRoom,
+        uint olthoiRoom,
+        uint societyRoom,
+        uint societyCelestialHandRoom,
+        uint societyEldrytchWebRoom,
+        uint societyRadiantBloodRoom)
+    {
+        Enabled                  = true;
+        AllegianceRoom           = allegianceRoom;
+        GeneralRoom              = generalRoom;
+        TradeRoom                = tradeRoom;
+        LfgRoom                  = lfgRoom;
+        RoleplayRoom             = roleplayRoom;
+        OlthoiRoom               = olthoiRoom;
+        SocietyRoom              = societyRoom;
+        SocietyCelestialHandRoom = societyCelestialHandRoom;
+        SocietyEldrytchWebRoom   = societyEldrytchWebRoom;
+        SocietyRadiantBloodRoom  = societyRadiantBloodRoom;
+    }
+
+    /// <summary>
+    /// Look up the runtime room id for a Turbine
+    /// <see cref="ChatChannelKindLite"/>. Returns 0 if the channel is not
+    /// available (server hasn't populated it / player not in society / etc).
+    /// </summary>
+    public uint RoomFor(ChatChannelKindLite kind) => kind switch
+    {
+        ChatChannelKindLite.Allegiance           => AllegianceRoom,
+        ChatChannelKindLite.General              => GeneralRoom,
+        ChatChannelKindLite.Trade                => TradeRoom,
+        ChatChannelKindLite.Lfg                  => LfgRoom,
+        ChatChannelKindLite.Roleplay             => RoleplayRoom,
+        ChatChannelKindLite.Olthoi               => OlthoiRoom,
+        ChatChannelKindLite.Society              => SocietyRoom,
+        ChatChannelKindLite.SocietyCelestialHand => SocietyCelestialHandRoom,
+        ChatChannelKindLite.SocietyEldrytchWeb   => SocietyEldrytchWebRoom,
+        ChatChannelKindLite.SocietyRadiantBlood  => SocietyRadiantBloodRoom,
+        _ => 0u,
+    };
+}
+
+/// <summary>
+/// Coarse Turbine channel selector usable from
+/// <see cref="TurbineChatState.RoomFor"/> without dragging in the
+/// AcDream.UI.Abstractions <c>ChatChannelKind</c> (which lives in a
+/// different layer). Maps 1:1 onto the chat-type-id values from
+/// holtburger turbine.rs (TurbineChatType, lines 31-45).
+/// </summary>
+public enum ChatChannelKindLite
+{
+    Allegiance,
+    General,
+    Trade,
+    Lfg,
+    Roleplay,
+    Society,
+    SocietyCelestialHand,
+    SocietyEldrytchWeb,
+    SocietyRadiantBlood,
+    Olthoi,
+}