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/HonorificHeader.cs

@@ -13,7 +13,8 @@ namespace HellionChat.Ui.Components;
 // bracketed title only appears when there is actually a title to show.
 internal sealed class HonorificHeader
 {
-    public const float Height = 30f;
+    // Scaled: MainWindow reserves body height against this, so it follows.
+    public static float Height => StyleEngine.Metrics.HonorificHeight;
 
     // SelfTest observables — set on the real Draw path so a headless step can
     // assert the gate/colour/truncation outcome instead of re-implementing it.
@@ -68,7 +69,11 @@ internal sealed class HonorificHeader
         using (_fonts.FontAwesome.Push())
         {
             crownWidth = ImGui.CalcTextSize(crownGlyph).X;
-            dl.AddText(origin + new Vector2(0f, 8f), crownColor, crownGlyph);
+            dl.AddText(
+                origin + new Vector2(0f, StyleEngine.Metrics.CenterY(Height)),
+                crownColor,
+                crownGlyph
+            );
         }
 
         // Gate the bracketed title through the 1.5.6 contract (toggle, IPC
@@ -92,12 +97,17 @@ internal sealed class HonorificHeader
             // TruncateToFitWidth measures the *Regular* font, so this must run
             // OUTSIDE the FontAwesome.Push block above (crownWidth was measured
             // inside it, which is correct).
-            var maxTitleWidth = maxWidth - crownWidth - 6f - 8f;
+            var gap = StyleEngine.Metrics.HonorificBracketGap;
+            var maxTitleWidth = maxWidth - crownWidth - gap - StyleEngine.Metrics.HonorificInset;
             if (maxTitleWidth > 0f)
             {
                 var rendered = StringUtil.TruncateToFitWidth($"«{current.Title}»", maxTitleWidth);
                 LastRenderedTitle = rendered;
-                dl.AddText(origin + new Vector2(crownWidth + 6f, 8f), titleColor, rendered);
+                dl.AddText(
+                    origin + new Vector2(crownWidth + gap, StyleEngine.Metrics.CenterY(Height)),
+                    titleColor,
+                    rendered
+                );
                 LastTitleRendered = true;
             }
         }

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;

HellionChat/Ui/Components/MessageList.cs

@@ -308,12 +308,17 @@ internal sealed class MessageList
         {
             // Scrolled into a gap: one full-height dummy keeps the scrollbar honest.
             var gap = CompensatedDummy(plan.LeadDummyHeight + plan.EndDummyHeight);
-            ImGui.Dummy(new Vector2(10f, gap));
+            ImGui.Dummy(new Vector2(StyleEngine.Metrics.MessageDummyWidth, gap));
             return;
         }
 
         if (plan.LeadDummyHeight > 0f)
-            ImGui.Dummy(new Vector2(10f, CompensatedDummy(plan.LeadDummyHeight)));
+            ImGui.Dummy(
+                new Vector2(
+                    StyleEngine.Metrics.MessageDummyWidth,
+                    CompensatedDummy(plan.LeadDummyHeight)
+                )
+            );
 
         for (var i = plan.FirstVisible; i <= plan.LastVisible; i++)
         {
@@ -329,7 +334,12 @@ internal sealed class MessageList
         }
 
         if (plan.EndDummyHeight > 0f)
-            ImGui.Dummy(new Vector2(10f, CompensatedDummy(plan.EndDummyHeight)));
+            ImGui.Dummy(
+                new Vector2(
+                    StyleEngine.Metrics.MessageDummyWidth,
+                    CompensatedDummy(plan.EndDummyHeight)
+                )
+            );
     }
 
     // First-frame / post-invalidation fallback: draw + measure every row into the