refactor: group ui/ statusbar and window subdirs

Continue tidying the flat ui/ root:

- ui/statusbar/: statusbar.rs becomes statusbar/mod.rs (its
  crate::ui::statusbar::* paths are preserved) and absorbs
  statusbar_config.rs + statusbar_menu.rs.
- ui/window/: the standalone manager/dialog windows move here —
  about, layout_manager, page_setup, plugin_manager, shortcuts,
  layers, update_notice, open_progress. The crate::ui::LayerPanel
  re-export is repointed so callers are unchanged.

Call sites repointed to the new paths; no compat re-exports beyond the
existing LayerPanel one. ui/ root drops from 21 to 10 flat files with
five subdirs (ribbon, style, popup, statusbar, window).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/ui/window/about.rs

@@ -0,0 +1,140 @@
+use crate::app::Message;
+use iced::widget::{button, column, container, row, text};
+use iced::{Background, Border, Color, Element, Theme};
+
+const BG: Color = Color {
+    r: 0.15,
+    g: 0.15,
+    b: 0.15,
+    a: 1.0,
+};
+const PANEL: Color = Color {
+    r: 0.12,
+    g: 0.12,
+    b: 0.12,
+    a: 1.0,
+};
+const BORDER: Color = Color {
+    r: 0.30,
+    g: 0.30,
+    b: 0.30,
+    a: 1.0,
+};
+const DIM: Color = Color {
+    r: 0.55,
+    g: 0.55,
+    b: 0.55,
+    a: 1.0,
+};
+const ACCENT: Color = Color {
+    r: 0.25,
+    g: 0.50,
+    b: 0.85,
+    a: 1.0,
+};
+const WHITE: Color = Color {
+    r: 0.92,
+    g: 0.92,
+    b: 0.92,
+    a: 1.0,
+};
+
+fn info_row<'a>(label: &'static str, value: String) -> Element<'a, Message> {
+    row![
+        text(label).size(11).color(DIM).width(100),
+        text(value).size(11).color(WHITE),
+    ]
+    .spacing(8)
+    .align_y(iced::Center)
+    .padding([3, 0])
+    .into()
+}
+
+pub fn view_window<'a>() -> Element<'a, Message> {
+    let version = env!("CARGO_PKG_VERSION");
+    let os = std::env::consts::OS;
+    let arch = std::env::consts::ARCH;
+
+    let logo = container(
+        column![
+            text("Open CAD Studio").size(32).color(ACCENT),
+            text("CAD application for Architecture & Engineering")
+                .size(11)
+                .color(DIM),
+        ]
+        .spacing(4)
+        .align_x(iced::Center),
+    )
+    .padding(iced::Padding {
+        top: 20.0,
+        right: 0.0,
+        bottom: 16.0,
+        left: 0.0,
+    })
+    .align_x(iced::Center);
+
+    let info_block = container(
+        column![
+            info_row("Version", format!("v{}", version)),
+            info_row("Platform", os.to_string()),
+            info_row("Arch", arch.to_string()),
+        ]
+        .spacing(2)
+        .padding([12, 16]),
+    )
+    .style(|_: &Theme| container::Style {
+        background: Some(Background::Color(PANEL)),
+        border: Border {
+            color: BORDER,
+            width: 1.0,
+            radius: 4.0.into(),
+        },
+        ..Default::default()
+    });
+
+    let copy_btn = button(text("Copy Info").size(11))
+        .on_press(Message::AboutCopyInfo)
+        .style(|_: &Theme, st| button::Style {
+            background: Some(Background::Color(match st {
+                button::Status::Hovered | button::Status::Pressed => Color {
+                    r: 0.20,
+                    g: 0.42,
+                    b: 0.72,
+                    a: 1.0,
+                },
+                _ => ACCENT,
+            })),
+            text_color: WHITE,
+            border: Border {
+                radius: 4.0.into(),
+                ..Default::default()
+            },
+            ..Default::default()
+        })
+        .padding([6, 16]);
+
+    let footer = row![copy_btn]
+        .align_y(iced::Center)
+        .padding(iced::Padding {
+            top: 12.0,
+            right: 0.0,
+            bottom: 0.0,
+            left: 0.0,
+        });
+
+    container(
+        column![logo, info_block, footer]
+            .spacing(0)
+            .padding(iced::Padding {
+                top: 0.0,
+                right: 20.0,
+                bottom: 20.0,
+                left: 20.0,
+            }),
+    )
+    .style(|_: &Theme| container::Style {
+        background: Some(Background::Color(BG)),
+        ..Default::default()
+    })
+    .into()
+}