fix(ui): scale active-tab underline with DPI for crisp rendering (F7.2)

The 2px underline pill was hardcoded — at 125/150% DPI the surrounding
tab layout scaled with ImGuiHelpers.GlobalScale but the pill stayed
2px, so the line landed on sub-pixel boundaries and rendered as a
fuzzy band. Now: height scales with GlobalScale (clamped to >=1px),
and the DrawList coordinates round to physical pixels via MathF.Round
so the rect aligns with the framebuffer grid.

HellionChat/Ui/ChatLogWindow.cs

@@ -1637,17 +1637,21 @@ public sealed class ChatLogWindow : Window
                 continue;
 
             // Active-tab underline pill (2px accent). No native ImGui underline API,
-            // so we use a direct DrawList pass.
+            // so we use a direct DrawList pass. Pill height scales with GlobalScale
+            // and all coordinates round to physical pixels so the line stays crisp
+            // on 125/150% DPI setups instead of bleeding into a sub-pixel blur.
             {
                 var theme = Plugin.ThemeRegistry.Active;
                 var min = ImGui.GetItemRectMin();
                 var max = ImGui.GetItemRectMax();
-                const float pillHeight = 2f;
+                var pillHeight = MathF.Max(1f, MathF.Round(2f * ImGuiHelpers.GlobalScale));
+                var yBottom = MathF.Round(max.Y);
+                var yTop = yBottom - pillHeight;
                 ImGui
                     .GetWindowDrawList()
                     .AddRectFilled(
-                        new Vector2(min.X, max.Y - pillHeight),
-                        new Vector2(max.X, max.Y),
+                        new Vector2(MathF.Round(min.X), yTop),
+                        new Vector2(MathF.Round(max.X), yBottom),
                         ColourUtil.RgbaToAbgr(theme.Colors.Accent)
                     );
             }