feat(style): a lab window for the input-row decision

Four elements, three variants each, drawn side by side in real ImGui against the
live theme. Reachable with /hellion lab.

The alternative was drawing mockups, and mockups are what sent this cycle wrong
once already -- they predate the settings window learning that structure is
typography and only controls get a fill. A picture also cannot show the part that
matters most here: switching themes switches which variant works.

Everything it draws comes from helpers that were already in DrawListExtensions
and had almost no callers. DrawSlipPolygon and DrawVerticalGradient had one
between them, in SegmentedControl. DrawGlowBorder had none at all.

Temporary, and deliberately not behind DEBUG: the decision happens in the build
Flo runs. It comes out once the variants are picked.

HellionChat/Plugin.cs

@@ -112,6 +112,7 @@ public sealed class Plugin : IAsyncDalamudPlugin
 #if DEBUG
     internal Ui.Windows.WidgetGalleryWindow WidgetGallery { get; private set; } = null!;
 #endif
+    internal Ui.Windows.InputBarLabWindow InputBarLab { get; private set; } = null!;
     public FirstRunWizard FirstRunWizard { get; private set; } = null!;
     internal DebuggerWindow DebuggerWindow { get; private set; } = null!;
 
@@ -456,6 +457,7 @@ public sealed class Plugin : IAsyncDalamudPlugin
 #if DEBUG
         WidgetGallery = _host.Services.GetRequiredService<Ui.Windows.WidgetGalleryWindow>();
 #endif
+        InputBarLab = _host.Services.GetRequiredService<Ui.Windows.InputBarLabWindow>();
         DebuggerWindow = _host.Services.GetRequiredService<DebuggerWindow>();
         FirstRunWizard = _host.Services.GetRequiredService<FirstRunWizard>();
         ChannelPopoutPool = _host.Services.GetRequiredService<Ui.Windows.ChannelPopoutPool>();
@@ -1042,6 +1044,14 @@ public sealed class Plugin : IAsyncDalamudPlugin
             WidgetGallery.Toggle();
             return;
         }
+#endif
+
+        if (arg.Equals("lab", StringComparison.OrdinalIgnoreCase))
+        {
+            InputBarLab.Toggle();
+            return;
+        }
+#if DEBUG
 #endif
         if (arg.Equals("reset", StringComparison.OrdinalIgnoreCase))
         {