refactor(ui): scale the remaining layout constants

What blocks A to E did not already touch: the honorific header height and its
two offsets, the message list dummy widths, and the quick-button reserve in the
input bar.

The reserve is the one with visible consequences. At 150% the buttons grow with
the font while a fixed 130px column does not, so they stopped fitting.

The honorific offsets are centred rather than scaled. The 8f there was
(30 - 14) / 2 for the old font, structurally the same case as the sidebar: a
scaled constant keeps its mis-centering, a computed one does not.

HellionChat/Ui/Components/InputBar.cs

@@ -30,7 +30,10 @@ internal sealed class InputBar
     // they follow automatically. The pill's own metrics live in PillStyle now.
     public static float Height => StyleEngine.Metrics.InputBarHeight;
     private const int BufferCapacity = 500;
-    private const float QuickButtonsReserve = 130f;
+
+    // Scaled: the buttons themselves grow with the font, so a fixed reserve
+    // stops fitting them at 150%.
+    private static float QuickButtonsReserve => StyleEngine.Metrics.InputQuickButtonsReserve;
 
     private readonly SymbolPicker _symbolPicker;
     private readonly FontManager _fonts;