feat(ui): wire ThemeRegistry crossfade into PushGlobal

Switch picks a lerped AbgrCache during the 300ms crossfade window
(ReduceMotion bypass keeps the snap path). Plugin-load init path
switches to SwitchSilent so opening the plugin no longer fades from
the default theme. WindowBg/ChildBg RGBA path stays bound to the
user's per-window opacity override and never fades.

PushGlobal takes the ThemeRegistry as a parameter -- it is an instance
member on Plugin, not static, so the single Plugin.Draw call-site
threads it through alongside the active theme.

HellionChat/Infrastructure/Hosting/InitHostedServices.cs

@@ -19,7 +19,7 @@ internal sealed class ThemeRegistryInitHostedService(ThemeRegistry registry) : I
         // warm cache; otherwise the first Switch falls through to the built-in
         // default when Config.Theme points at a custom slug.
         foreach (var _ in registry.AllCustom()) { }
-        registry.Switch(Plugin.Config.Theme);
+        registry.SwitchSilent(Plugin.Config.Theme);
         return Task.CompletedTask;
     }
 

HellionChat/Plugin.cs

@@ -912,6 +912,7 @@ public sealed class Plugin : IAsyncDalamudPlugin
         // Theme engine is always active; Classic is a theme, not a disabled state.
         using IDisposable _style = HellionStyle.PushGlobal(
             ThemeRegistry.Active,
+            ThemeRegistry,
             Config.WindowOpacity
         );
 

HellionChat/Ui/HellionStyle.cs

@@ -33,11 +33,34 @@ internal static class HellionStyle
 
     // Global color and style stack pushed once per frame.
     // windowOpacity: window background alpha (0.5-1.0).
-    internal static IDisposable PushGlobal(Theme theme, float windowOpacity = 1.0f)
+    internal static IDisposable PushGlobal(
+        Theme theme,
+        ThemeRegistry registry,
+        float windowOpacity = 1.0f
+    )
     {
         var c = theme.Colors;
         var l = theme.Layout;
-        var a = theme.AbgrCache;
+
+        // Crossfade: PM-1 reads a lerped snapshot during the 300ms window
+        // following a Switch (TryGetActiveCrossfade returns false outside
+        // the window or while ReduceMotion is on). Only the ABGR-slot path
+        // crossfades -- WindowBg/ChildBg RGBA stays bound to the user's
+        // per-window opacity override and must not fade. See
+        // feedback_dalamud_pinning_override.
+        ThemeAbgrCache a;
+        if (
+            !Plugin.Config.ReduceMotion
+            && registry.TryGetActiveCrossfade(out var lerped)
+        )
+        {
+            a = lerped;
+        }
+        else
+        {
+            a = theme.AbgrCache;
+        }
+
         var stack = new StackHandle();
 
         var alphaByte = (uint)Math.Clamp((int)(windowOpacity * 255f), 0x55, 0xFF);