fix: trade gate round 4 - "The trade has been cancelled." + retail's

staged-item trading marker

- Cancel text: ClientTradeSystem::Handle_Trade__Recv_CloseTrade
  @0x0056DE30 shows "The trade has been cancelled." UNCONDITIONALLY
  (every close reason) as 0x1A ClientLocal - the yellow top-center
  SpewBox line. Wired at the router's onTradeClose beside ApplyClose;
  the string lives in ClientTextRefusals with its citation.
- Staged-item marker: retail's mechanism decoded end-to-end - the
  UIItem prototype (catalog 0x21000037) authors overlay child
  0x10000438 (sprite 0x06001DAE, the green frame + corner trade icon),
  bound @0x004E18FC and SetVisible(tradeState != 0) @0x004E2420;
  gmSecureTradeUI::AddItem @0x004CA801 sets
  ACCWeenieObject::SetTradeState(1) on YOUR staged items. Ported as:
  UiItemSlot.ShowTradeOverlay + TradeOverlaySprite (drawn over the
  icon), set on the trade window's self-grid cells; and
  RuntimeTradeState now borrows the canonical object table and
  maintains ClientObject.TradeState (1 at stage, 0 at remove/failure/
  reset/close/clear) - which also brings the ALREADY-PORTED placement
  policy's "You cannot move an item while it is being traded" refusal
  to life (its input field previously had no live producer).

Runtime 1,626, App 4,992/3 - green.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/AcDream.Core/Chat/ClientTextRefusals.cs

@@ -65,6 +65,13 @@ public static class ClientTextRefusals
     /// </summary>
     public const string CantJumpRecent = "You've jumped too recently!";
 
+    /// <summary>
+    /// <c>ClientTradeSystem::Handle_Trade__Recv_CloseTrade @ 0x0056DE30</c>
+    /// — shown UNCONDITIONALLY (every close reason) as LogTextType 0x1A
+    /// ClientLocal, the yellow top-center SpewBox line.
+    /// </summary>
+    public const string TradeCancelled = "The trade has been cancelled.";
+
     /// <summary>
     /// <c>WeenieError.YouAreTooTiredToDoThat (0x003E)</c> —
     /// <c>CommandInterpreter::MovePlayer</c>'s stamina-exhausted refusal