@

fix(D.2b): channel menu popup opaque + button label tracks selected target

- the popup inherited the chat window 0.75 opacity so the transcript bled through;
  add UiRenderContext.PushAlphaAbsolute and draw the popup at absolute opacity.
- the "Chat" button was hardcoded; it now shows the active talk target (retail
  updates it on selection). Exact textured menu-panel sprite is a follow-up (the
  popup is a keystone UIElement_Menu construct, not in the chat LayoutDesc).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
@

src/AcDream.App/UI/UiRenderContext.cs

@@ -34,6 +34,10 @@ public sealed class UiRenderContext
     /// <summary>Multiply <paramref name="a"/> into the running opacity. Pair with <see cref="PopAlpha"/>.</summary>
     public void PushAlpha(float a) { _alphaStack.Add(_alpha); _alpha *= a; }
 
+    /// <summary>Push an ABSOLUTE opacity (replaces, not multiplies) — for popups/overlays
+    /// that must stay opaque even inside a translucent window. Pair with <see cref="PopAlpha"/>.</summary>
+    public void PushAlphaAbsolute(float a) { _alphaStack.Add(_alpha); _alpha = a; }
+
     public void PopAlpha()
     {
         if (_alphaStack.Count == 0) return;