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>

src/AcDream.UI.Abstractions/ChatChannelKind.cs

@@ -0,0 +1,40 @@
+namespace AcDream.UI.Abstractions;
+
+/// <summary>
+/// Outbound chat channel selector. Mirrors holtburger's <c>ChatChannelKind</c>
+/// (<c>references/holtburger/crates/holtburger-core/src/client/types.rs</c>
+/// lines 35-49) plus a synthetic <see cref="Say"/> + <see cref="Tell"/> for
+/// the two non-channel cases — local speech and whispers — so a single
+/// <see cref="SendChatCmd"/> can carry every outbound flavour the chat
+/// panel emits.
+///
+/// <para>
+/// Channels split into:
+/// <list type="bullet">
+/// <item><b>Legacy</b> (Fellowship..CoVassals): map to a fixed <c>ChatChannel</c>
+///     bitflag id via <see cref="ChannelResolver"/> and ride 0x0147 ChatChannel.</item>
+/// <item><b>Turbine</b> (General..Olthoi): require a TurbineChat channel id
+///     resolved at runtime — not yet wired (Phase I.6 owns TurbineChat).</item>
+/// <item><b>Say</b> / <b>Tell</b>: route to the dedicated 0x0015 / 0x005D
+///     opcodes — no channel id needed.</item>
+/// </list>
+/// </para>
+/// </summary>
+public enum ChatChannelKind
+{
+    Say,
+    Tell,
+    Fellowship,
+    Allegiance,
+    Vassals,
+    Patron,
+    Monarch,
+    CoVassals,
+    General,
+    Trade,
+    Lfg,
+    Roleplay,
+    Society,
+    Olthoi,
+    Unknown,
+}