refactor(ui): centralize hdivider/vsep in style::form

Deduplicate the byte-identical 1px divider helpers previously copy-pasted across 6 modules. form::{hdivider, vseparator} is now canonical, with a form::vsep alias for legacy call sites. style_manager re-exports both so scale_manager and anno_object_scale imports keep working unchanged. Delete locals in style_manager, plotstyle, dimstyle, layout_manager, attribute_editor. Replace thin wrappers in window/plot with direct imports. no visual change.

src/ui/style/dimstyle.rs

@@ -6,6 +6,7 @@ use iced::widget::{
 };
 use iced::{mouse, Background, Border, Element, Length, Point, Rectangle, Theme};
 use crate::ui::style::common::muted_style;
+use crate::ui::style::form::hdivider;
 use crate::t;
 use std::borrow::Cow;
 use std::fmt;
@@ -263,19 +264,6 @@ impl canvas::Program<Message> for DimensionPreview {
     }
 }
 
-fn hdivider<'a>(width: iced::Length) -> Element<'a, Message> {
-    container(Space::new().width(width).height(1))
-        .width(width)
-        .height(1)
-        .style(|theme: &Theme| container::Style {
-            background: Some(Background::Color(
-                theme.palette().background.neutral.color
-            )),
-            ..Default::default()
-        })
-        .into()
-}
-
 pub fn view_window<'a>(
     styles: Vec<String>,
     selected: &'a str,

src/ui/style/form.rs

@@ -83,6 +83,12 @@ pub fn vseparator<'a>(height: Length) -> Element<'a, Message> {
         .into()
 }
 
+/// Alias kept for call sites that historically used `vsep`.
+/// Same implementation as [`vseparator`].
+pub fn vsep<'a>(height: Length) -> Element<'a, Message> {
+    vseparator(height)
+}
+
 /// Muted section heading.
 pub fn section_label<'a>(label: Cow<'static, str>) -> Element<'a, Message> {
     text(label).size(11).style(muted_style).into()

src/ui/style/plotstyle.rs

@@ -4,6 +4,7 @@ use crate::app::Message;
 use iced::widget::{button, column, container, row, scrollable, text, text_input, Space};
 use iced::{Background, Border, Element, Theme};
 use crate::ui::style::common::muted_style;
+use crate::ui::style::form::{hdivider, vsep};
 use crate::t;
 use std::borrow::Cow;
 use std::fmt;
@@ -83,32 +84,6 @@ fn field_style(theme: &Theme, status: text_input::Status) -> text_input::Style {
     }
 }
 
-fn hdivider<'a>(width: iced::Length) -> Element<'a, Message> {
-    container(Space::new().width(width).height(1))
-        .width(width)
-        .height(1)
-        .style(|theme: &Theme| container::Style {
-            background: Some(Background::Color(
-                theme.palette().background.neutral.color
-            )),
-            ..Default::default()
-        })
-        .into()
-}
-
-fn vsep<'a>(height: iced::Length) -> Element<'a, Message> {
-    container(Space::new().width(1).height(height))
-        .width(1)
-        .height(height)
-        .style(|theme: &Theme| container::Style {
-            background: Some(Background::Color(
-                theme.palette().background.neutral.color
-            )),
-            ..Default::default()
-        })
-        .into()
-}
-
 pub fn view_window<'a>(
     document: &'a acadrust::CadDocument,
     table: Option<&'a crate::io::plot_style::PlotStyleTable>,

src/ui/style/style_manager.rs

@@ -327,28 +327,4 @@ pub(crate) fn muted_text_style(theme: &Theme) -> iced::widget::text::Style {
     crate::ui::style::common::muted_style(theme)
 }
 
-pub(crate) fn hdivider<'a>(width: iced::Length) -> Element<'a, Message> {
-    container(Space::new().width(width).height(1))
-        .width(width)
-        .height(1)
-        .style(|theme: &Theme| container::Style {
-            background: Some(Background::Color(
-                theme.palette().background.neutral.color
-            )),
-            ..Default::default()
-        })
-        .into()
-}
-
-pub(crate) fn vsep<'a>(height: iced::Length) -> Element<'a, Message> {
-    container(Space::new().width(1).height(height))
-        .width(1)
-        .height(height)
-        .style(|theme: &Theme| container::Style {
-            background: Some(Background::Color(
-                theme.palette().background.neutral.color
-            )),
-            ..Default::default()
-        })
-        .into()
-}
+pub(crate) use crate::ui::style::form::{hdivider, vsep};