feat(ui+net): #16 LiveCommandBus + WorldSession.Send{Talk,Tell,Channel} + SendChatCmd wiring

Replaces NullCommandBus.Instance in PanelContext with a real
LiveCommandBus when a live session is active. Panels publish
SendChatCmd; the host routes it to the right wire opcode + emits
a ChatLog.OnSelfSent local echo (optimistic; retail-equivalent
for Talk).

Pieces:
- ChatChannelKind enum (UI.Abstractions) - mirrors holtburger's
  ChatChannelKind (references/holtburger/.../client/types.rs:35-49).
- SendChatCmd record (UI.Abstractions) - (Channel, TargetName?, Text).
- LiveCommandBus (UI.Abstractions) - single-handler-per-type;
  Register<T> throws on double-register; Publish<T> logs missing
  handler but does not throw.
- ChannelResolver (UI.Abstractions) - port of holtburger's
  resolve_legacy_channel (client/commands.rs:50-62) mapping
  ChatChannelKind to legacy ChatChannel ids verbatim from
  holtburger-protocol/.../chat/types.rs:8-24 (Fellow=0x0800,
  AllegianceBroadcast=0x02000000, Vassals=0x1000, Patron=0x2000,
  Monarch=0x4000, CoVassals=0x01000000).
- WorldSession.SendTalk / SendTell / SendChannel - 3-line wrappers
  around existing ChatRequests.Build* + SendGameAction. Internal
  GameActionCapture seam + InternalsVisibleTo for tests.
- GameWindow registers SendChatCmd handler: Say -> SendTalk +
  ChatLog echo, Tell -> SendTell + echo, channel kinds ->
  ChannelResolver.Resolve -> SendChannel + echo.

12 new tests across SendChatCmd + LiveCommandBus + ChannelResolver
+ WorldSessionChat. NullCommandBus.Instance retained for back-compat
when no live session.

Solution total: 893 green (51 + 229 + 613).

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

tests/AcDream.UI.Abstractions.Tests/SendChatCmdTests.cs

@@ -0,0 +1,33 @@
+namespace AcDream.UI.Abstractions.Tests;
+
+public sealed class SendChatCmdTests
+{
+    [Fact]
+    public void Construct_DefaultsTargetNameToNull_ForNonTellChannels()
+    {
+        var cmd = new SendChatCmd(ChatChannelKind.Say, TargetName: null, Text: "hello");
+
+        Assert.Equal(ChatChannelKind.Say, cmd.Channel);
+        Assert.Null(cmd.TargetName);
+        Assert.Equal("hello", cmd.Text);
+    }
+
+    [Fact]
+    public void Equality_HoldsForRecordsWithSameValues()
+    {
+        var a = new SendChatCmd(ChatChannelKind.Tell, "Alice", "hi");
+        var b = new SendChatCmd(ChatChannelKind.Tell, "Alice", "hi");
+
+        Assert.Equal(a, b);
+        Assert.Equal(a.GetHashCode(), b.GetHashCode());
+    }
+
+    [Fact]
+    public void Equality_DiffersWhenChannelDiffers()
+    {
+        var a = new SendChatCmd(ChatChannelKind.Fellowship, null, "raid time");
+        var b = new SendChatCmd(ChatChannelKind.Allegiance, null, "raid time");
+
+        Assert.NotEqual(a, b);
+    }
+}