feat(runtime): share chat commands and run login sequence

src/AcDream.Runtime/Chat/ICommandBus.cs

@@ -0,0 +1,24 @@
+namespace AcDream.Runtime.Chat;
+
+/// <summary>
+/// Publishes user-intent commands from panels to the systems that handle
+/// them (WorldSession, ChatService, Inventory, ...). Panels never touch
+/// those systems directly — they <see cref="Publish{T}(T)"/> a record
+/// and the bus dispatches.
+///
+/// <para>
+/// D.2a scaffolding: <see cref="NullCommandBus"/> is the default wire-up
+/// — commands are accepted but dropped. Real routing lands alongside
+/// chat and inventory (Sprint 2 of the UI plan) when we actually need
+/// commands flowing server-ward.
+/// </para>
+/// </summary>
+public interface ICommandBus
+{
+    /// <summary>
+    /// Publish a command record. The bus routes by runtime type via
+    /// registered handlers. Never blocks; handlers run on the publish
+    /// thread today (render thread for panel-triggered commands).
+    /// </summary>
+    void Publish<T>(T command) where T : notnull;
+}