feat(statusbar): customizable pills with coordinates and clean screen

Add a customization menu (far-right handle) that lists every status-bar
pill with a check mark; toggling a row shows or hides that pill, and the
choice persists across sessions in the config dir.

New pills:
- Coordinates: live cursor readout (re-adds the model-space world offset
  so it shows true drawing coordinates), updated on every move rather
  than only while a command is active.
- Clean Screen: hide the ribbon and side panels for a full canvas.

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

src/ui/statusbar_menu.rs

@@ -0,0 +1,117 @@
+//! Status-bar customization menu — a checkmark list of every toggle pill,
+//! opened from the bar's far-right handle. Rendered as a floating overlay
+//! above the status bar, same pattern as the scale picker.
+
+use iced::widget::{button, column, container, mouse_area, row, text};
+use iced::{Background, Border, Color, Element, Fill, Length, Padding, Theme};
+
+use crate::app::Message;
+use crate::ui::statusbar_config::{StatusBarConfig, StatusPill};
+
+/// Full-screen overlay: transparent click-catcher + the menu panel pinned to
+/// the bottom-right, just above the status bar.
+pub fn statusbar_menu_overlay(config: &StatusBarConfig) -> Element<'static, Message> {
+    let rows: Vec<Element<'static, Message>> = StatusPill::ALL
+        .iter()
+        .map(|&pill| {
+            menu_row(
+                pill.label(),
+                config.is_visible(pill),
+                Message::ToggleStatusPill(pill),
+            )
+        })
+        .collect();
+
+    let panel = container(column(rows))
+        .style(|_: &Theme| container::Style {
+            background: Some(Background::Color(PANEL_BG)),
+            border: Border {
+                color: PANEL_BORDER,
+                width: 1.0,
+                radius: 3.0.into(),
+            },
+            ..Default::default()
+        })
+        .width(Length::Fixed(200.0));
+
+    let positioned = container(panel)
+        .align_right(Fill)
+        .align_bottom(Fill)
+        .padding(Padding {
+            bottom: 27.0,
+            right: 4.0,
+            top: 0.0,
+            left: 0.0,
+        })
+        .width(Fill)
+        .height(Fill);
+
+    mouse_area(positioned)
+        .on_press(Message::CloseStatusBarMenu)
+        .into()
+}
+
+fn menu_row(label: &'static str, checked: bool, msg: Message) -> Element<'static, Message> {
+    let check = text(if checked { "✓" } else { "  " })
+        .size(11)
+        .color(if checked { CHECK_COLOR } else { Color::TRANSPARENT })
+        .width(Length::Fixed(14.0));
+
+    let lbl = text(label)
+        .size(11)
+        .color(if checked { LABEL_ON } else { LABEL_OFF });
+
+    let content = row![check, lbl].spacing(6).align_y(iced::Center);
+
+    button(content)
+        .on_press(msg)
+        .style(|_: &Theme, status| button::Style {
+            background: Some(Background::Color(match status {
+                button::Status::Hovered => ROW_HOVER,
+                _ => Color::TRANSPARENT,
+            })),
+            ..Default::default()
+        })
+        .width(Fill)
+        .padding([4, 10])
+        .into()
+}
+
+// ── Colours ───────────────────────────────────────────────────────────────
+
+const PANEL_BG: Color = Color {
+    r: 0.15,
+    g: 0.15,
+    b: 0.15,
+    a: 1.0,
+};
+const PANEL_BORDER: Color = Color {
+    r: 0.32,
+    g: 0.32,
+    b: 0.32,
+    a: 1.0,
+};
+const ROW_HOVER: Color = Color {
+    r: 0.22,
+    g: 0.22,
+    b: 0.22,
+    a: 1.0,
+};
+const CHECK_COLOR: Color = Color {
+    r: 0.35,
+    g: 0.75,
+    b: 1.00,
+    a: 1.0,
+};
+const LABEL_ON: Color = Color {
+    r: 0.92,
+    g: 0.92,
+    b: 0.92,
+    a: 1.0,
+};
+const LABEL_OFF: Color = Color {
+    r: 0.65,
+    g: 0.65,
+    b: 0.65,
+    a: 1.0,
+};