refactor(style): dedup layers/xref row-button style into ui::style::row_button

Moves the byte-identical zebra/selected cell-button bodies from layers.rs and xref_manager.rs plus the layers header-button body into one shared module. All six call sites now use the shared helpers; toolbar_btn helpers untouched (different semantics). No new tests per owner request (pure move, verified by build plus full suite before test removal).

src/ui/window/layers.rs

@@ -3,6 +3,7 @@
 use crate::app::Message;
 use crate::ui::properties::{lw_options, LinetypeItem, LwItem};
 use crate::ui::style::common::muted_style;
+use crate::ui::style::row_button::{cell_button_style, header_button_style};
 use crate::ui::ROW_H;
 use codec::tables::layer::Layer as DocLayer;
 use codec::tables::Table;
@@ -503,48 +504,6 @@ impl LayerPanel {
 
 // ── Sorting helpers ─────────────────────────────────────────────────────────
 
-fn layer_cell_button_style(
-    theme: &Theme,
-    status: button::Status,
-    is_selected: bool,
-    index: usize,
-) -> button::Style {
-    let palette = theme.palette();
-    let highlighted = matches!(status, button::Status::Hovered);
-    let pair = if highlighted {
-        palette.background.strong
-    } else if is_selected {
-        palette.primary.weak
-    } else if index % 2 == 0 {
-        palette.background.base
-    } else {
-        palette.background.weak
-    };
-    button::Style {
-        background: highlighted.then_some(Background::Color(pair.color)),
-        text_color: pair.text,
-        ..Default::default()
-    }
-}
-
-fn layer_header_button_style(theme: &Theme, status: button::Status) -> button::Style {
-    let palette = theme.palette();
-    let highlighted = matches!(
-        status,
-        button::Status::Hovered | button::Status::Pressed
-    );
-    let pair = if highlighted {
-        palette.background.strong
-    } else {
-        palette.background.weak
-    };
-    button::Style {
-        background: highlighted.then_some(Background::Color(pair.color)),
-        text_color: pair.text,
-        ..Default::default()
-    }
-}
-
 /// Packed RGB key for ordering colours deterministically by hue-ish bytes.
 fn color_sort_key(c: AcadColor) -> u32 {
     let c = iced_color_from_acad(&c);
@@ -573,7 +532,7 @@ fn sortable_header<'a>(
     }
     button(content)
         .on_press(Message::LayerSort(col))
-        .style(layer_header_button_style)
+        .style(header_button_style)
         .padding(Padding {
             top: 0.0,
             bottom: 0.0,
@@ -717,9 +676,7 @@ fn layer_row<'a>(
     let svg_btn = |bytes: &'static [u8], on_press: Message| -> Element<'a, Message> {
         button(crate::ui::icons::semantic(bytes, ICON_SZ))
         .on_press(on_press)
-        .style(move |theme: &Theme, status| {
-            layer_cell_button_style(theme, status, is_selected, index)
-        })
+        .style(cell_button_style(is_selected, index))
         .padding(Padding {
             top: COMBO_PAD_V,
             bottom: COMBO_PAD_V,
@@ -747,9 +704,7 @@ fn layer_row<'a>(
 
     let plot_btn: Element<'_, Message> = button(plot_icon)
         .on_press(Message::LayerTogglePlot(index))
-        .style(move |theme: &Theme, status| {
-            layer_cell_button_style(theme, status, is_selected, index)
-        })
+        .style(cell_button_style(is_selected, index))
         .padding(Padding {
             top: COMBO_PAD_V,
             bottom: COMBO_PAD_V,
@@ -788,9 +743,7 @@ fn layer_row<'a>(
                 .size(FONT_SZ),
         )
         .on_press(Message::LayerRenameStart(index))
-        .style(move |theme: &Theme, status| {
-            layer_cell_button_style(theme, status, is_selected, index)
-        })
+        .style(cell_button_style(is_selected, index))
         .padding(Padding {
             top: COMBO_PAD_V,
             bottom: COMBO_PAD_V,