feat(chat): Phase H.1 Talk/Tell/ChatChannel + HearSpeech + ChatLog

Completes the chat-wire layer end-to-end: outbound Talk (/say), Tell
(/tell), ChatChannel, + inbound HearSpeech (0x02BB) / HearRangedSpeech
(0x02BC) routed into a unified ChatLog that also consumes the already-
parsed GameEvent ChannelBroadcast / Tell / TransientMessage / Popup.

Wire layer (AcDream.Core.Net/Messages):
- ChatRequests.BuildTalk (0x0015, inside 0xF7B1): gameActionSequence
  + string16L message. PackString16L helper with 4-byte pad.
- ChatRequests.BuildTell (0x005D): targetName + message, each
  string16L with its own padding.
- ChatRequests.BuildChatChannel (0x0147): channelId + message.
- HearSpeech.TryParse handles BOTH 0x02BB local AND 0x02BC ranged —
  single parser with IsRanged flag in the returned record. Standalone
  GameMessage (NOT wrapped in 0xF7B0).

WorldSession integration:
- ProcessDatagram branch for HearSpeech.LocalOpcode /
  HearSpeech.RangedOpcode; fires new SpeechHeard event.
- Places the new branch before the 0xF7B0 GameEvent branch so ordering
  stays stable.

Core layer (AcDream.Core/Chat):
- ChatEntry record: (Kind, Sender, Text, SenderGuid, ChannelId, Received).
- ChatKind enum: LocalSpeech, RangedSpeech, Channel, Tell, System, Popup.
- ChatLog: ring-buffer (default 500) of entries; adapters for every
  inbound source (OnLocalSpeech, OnChannelBroadcast, OnTellReceived,
  OnSystemMessage, OnPopup) plus OnSelfSent for echoing outbound.
  Fires EntryAppended so UI panel can scroll / highlight.

Tests (15 new):
- ChatRequests: Talk / Tell / ChatChannel byte-exact encoding (including
  string16L padding edge cases).
- HearSpeech: local + ranged round-trip, wrong-opcode returns null.
- ChatLog: local / ranged / channel / tell / system / self echo,
  ring-buffer drops oldest, Clear empties.

Build green, 570 tests pass (up from 555).

With the chat wire layer in place, Phase H.1's "chat window panel"
(UI slice 05) is purely a UI task: instantiate ChatLog, bind to
EntryAppended, feed rows into the retail-UI widget toolkit. No more
protocol gaps.

Ref: r08 §3 (opcodes 0x0015, 0x005D, 0x0147), §2 (0x02BB, 0x02BC).
Ref: ACE GameMessageHearSpeech.cs + GameActionChannelBroadcast.cs.

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

src/AcDream.Core/Chat/ChatLog.cs

@@ -0,0 +1,142 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.Concurrent;
+
+namespace AcDream.Core.Chat;
+
+/// <summary>
+/// Unified chat log — mirrors every chat-bearing message the server
+/// sends (local HearSpeech, broadcast ChannelBroadcast, whispered
+/// Tell, system TransientMessage, PopupString).
+///
+/// <para>
+/// Sits behind the UI chat panel (Phase D.2) and the scripting
+/// plugin API so plugins can react to chat (e.g. auto-reply, loot
+/// logging).
+/// </para>
+///
+/// <para>
+/// Retail keeps ~200 lines of scrollback. Our ring buffer defaults to
+/// 500 and is configurable.
+/// </para>
+/// </summary>
+public sealed class ChatLog
+{
+    private readonly ConcurrentQueue<ChatEntry> _buffer = new();
+    private readonly int _maxEntries;
+
+    public ChatLog(int maxEntries = 500)
+    {
+        if (maxEntries < 1) throw new ArgumentOutOfRangeException(nameof(maxEntries));
+        _maxEntries = maxEntries;
+    }
+
+    /// <summary>Fires every time a new entry is appended.</summary>
+    public event Action<ChatEntry>? EntryAppended;
+
+    /// <summary>Snapshot of all current entries, oldest first.</summary>
+    public ChatEntry[] Snapshot() => _buffer.ToArray();
+
+    public int Count => _buffer.Count;
+
+    // ── Inbound adapters ─────────────────────────────────────────────────────
+
+    /// <summary>Local or ranged HearSpeech (0x02BB / 0x02BC).</summary>
+    public void OnLocalSpeech(string sender, string text, uint senderGuid, bool isRanged)
+    {
+        Append(new ChatEntry(
+            Kind: isRanged ? ChatKind.RangedSpeech : ChatKind.LocalSpeech,
+            Sender: sender,
+            Text: text,
+            SenderGuid: senderGuid,
+            ChannelId: 0));
+    }
+
+    /// <summary>GameEvent ChannelBroadcast (0x0147).</summary>
+    public void OnChannelBroadcast(uint channelId, string sender, string text)
+    {
+        Append(new ChatEntry(
+            Kind: ChatKind.Channel,
+            Sender: sender,
+            Text: text,
+            SenderGuid: 0,
+            ChannelId: channelId));
+    }
+
+    /// <summary>GameEvent Tell (0x02BD) — whisper received.</summary>
+    public void OnTellReceived(string sender, string text, uint senderGuid)
+    {
+        Append(new ChatEntry(
+            Kind: ChatKind.Tell,
+            Sender: sender,
+            Text: text,
+            SenderGuid: senderGuid,
+            ChannelId: 0));
+    }
+
+    /// <summary>GameEvent CommunicationTransientString (0x02EB) — e.g. "Your spell fizzled!"</summary>
+    public void OnSystemMessage(string text, uint chatType)
+    {
+        Append(new ChatEntry(
+            Kind: ChatKind.System,
+            Sender: "",
+            Text: text,
+            SenderGuid: 0,
+            ChannelId: chatType));
+    }
+
+    /// <summary>GameEvent PopupString (0x0004) — modal dialog text.</summary>
+    public void OnPopup(string text)
+    {
+        Append(new ChatEntry(
+            Kind: ChatKind.Popup,
+            Sender: "",
+            Text: text,
+            SenderGuid: 0,
+            ChannelId: 0));
+    }
+
+    /// <summary>Echo the player's own outbound message after local send.</summary>
+    public void OnSelfSent(ChatKind kind, string text, string targetOrChannel = "")
+    {
+        Append(new ChatEntry(
+            Kind: kind,
+            Sender: targetOrChannel,    // used as "to whom" for Tell / channel name for Channel
+            Text: text,
+            SenderGuid: 0,
+            ChannelId: 0));
+    }
+
+    private void Append(ChatEntry entry)
+    {
+        _buffer.Enqueue(entry);
+        while (_buffer.Count > _maxEntries)
+            _buffer.TryDequeue(out _);
+        EntryAppended?.Invoke(entry);
+    }
+
+    public void Clear()
+    {
+        while (_buffer.TryDequeue(out _)) { /* drain */ }
+    }
+}
+
+public enum ChatKind
+{
+    LocalSpeech,
+    RangedSpeech,
+    Channel,
+    Tell,
+    System,
+    Popup,
+}
+
+public readonly record struct ChatEntry(
+    ChatKind Kind,
+    string Sender,
+    string Text,
+    uint SenderGuid,
+    uint ChannelId)
+{
+    public DateTime Received { get; init; } = DateTime.UtcNow;
+}