Align ByLayer property dropdowns consistently in Properties panel

Use SELECTOR_PAD_V (calculated from ROW_H and FONT_SZ) instead of
hardcoded [3, 6] padding for color selector buttons. This matches the
padding used by combo_box widgets for Lineweight and Linetype,
ensuring all three ByLayer dropdowns align vertically and have
consistent height.

Fixes #1047

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/ui/color_select.rs

@@ -5,11 +5,17 @@
 
 use crate::app::Message;
 use crate::ui::properties::acad_color_display;
+use crate::ui::ROW_H;
 use acadrust::types::Color as AcadColor;
 use iced::widget::{button, column, container, row, text};
-use iced::{Background, Border, Color, Element, Length, Theme};
+use iced::{Background, Border, Color, Element, Length, Padding, Theme};
 use crate::t;
 
+/// Font size for color selector buttons (matches combo_box styling).
+const FONT_SZ: f32 = ROW_H * 0.42;
+/// Vertical padding for color selector buttons (matches combo_box styling).
+const SELECTOR_PAD_V: f32 = (ROW_H - FONT_SZ * 1.3 - 2.0) / 2.0;
+
 /// Which "logical" entries the colour list offers besides the standard ACI
 /// colours.
 #[derive(Clone, Copy, Default)]
@@ -222,7 +228,12 @@ fn color_selector_with_indicator<'a>(
         .align_y(iced::Center),
     )
     .on_press(on_toggle)
-    .padding([3, 6])
+    .padding(Padding {
+        top: SELECTOR_PAD_V,
+        bottom: SELECTOR_PAD_V,
+        left: 6.0,
+        right: 6.0,
+    })
     .width(Length::Fill);
 
     if !open {