feat(polar): angle picker dropdown on the POLAR pill (#264)

The polar-tracking pill only right-click-cycled 15→30→45→90. Add an
AutoCAD-style angle picker opened from a caret on the pill: presets
90/45/30/22.5/18/15/10/5/1 plus a free-text field for any custom angle,
mirroring the existing units / scale status-bar popups. The chosen angle
persists like the other user settings.

Factor the shared chrome into one `split_pill(main, caret_msg, active,
open)` helper (+ `pill_text_color`) so the OSNAP and POLAR pills stop
hand-rolling the same outer border, background, caret and sizing — each
pill now only supplies its own main region. The caret is sized and
aligned to sit inside the single pill border on both.

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

src/ui/popup/mod.rs

@@ -1,5 +1,6 @@
 pub mod cycle_popup;
 pub mod isolate_popup;
+pub mod polar_popup;
 pub mod scale_popup;
 pub mod selection_filter_popup;
 pub mod snap_popup;

src/ui/popup/polar_popup.rs

@@ -0,0 +1,138 @@
+//! Polar-tracking angle picker — sets the polar increment used by POLAR
+//! tracking. Rendered as a floating overlay above the status bar, same pattern
+//! as the units / scale pickers. Offers the common AutoCAD-style increments
+//! plus a free-text field for any custom angle (#264).
+
+use iced::widget::{button, column, container, mouse_area, row, text, text_input};
+use iced::{Background, Border, Color, Element, Fill, Length, Rectangle, Theme};
+
+use crate::app::Message;
+
+/// Angle increments offered in the picker, in degrees. Matches the common
+/// drafting set and adds the fine 1° step requested in #264.
+const PRESETS: &[f32] = &[90.0, 45.0, 30.0, 22.5, 18.0, 15.0, 10.0, 5.0, 1.0];
+
+/// Format an angle without a trailing `.0` (so `22.5°` but `15°`).
+pub fn angle_label(deg: f32) -> String {
+    if (deg.fract()).abs() < 1e-3 {
+        format!("{:.0}°", deg)
+    } else {
+        format!("{deg}°")
+    }
+}
+
+/// Full-screen overlay: transparent click-catcher + angle list pinned
+/// bottom-right, above the status bar. `custom` is the live text of the
+/// free-entry field.
+pub fn polar_popup_overlay<'a>(
+    current: f32,
+    custom: &'a str,
+    pill: Option<Rectangle>,
+    win: (f32, f32),
+) -> Element<'a, Message> {
+    let mut rows: Vec<Element<'a, Message>> = PRESETS
+        .iter()
+        .map(|&deg| {
+            let active = (current - deg).abs() < 1e-3;
+            angle_row(deg, active)
+        })
+        .collect();
+
+    // Free-entry custom angle: type a value and press Enter to apply.
+    let custom_field = text_input("Custom…", custom)
+        .on_input(Message::PolarCustomInput)
+        .on_submit(Message::SubmitPolarCustom)
+        .size(11)
+        .padding([2, 6])
+        .width(Length::Fixed(58.0));
+    let custom_row = container(
+        row![
+            custom_field,
+            text("°").size(11).color(LABEL_OFF),
+        ]
+        .spacing(4)
+        .align_y(iced::Center),
+    )
+    .padding([5, 10]);
+    rows.push(custom_row.into());
+
+    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(120.0));
+
+    let positioned = super::position_statusbar_popup(panel.into(), pill, win, 120.0, true);
+
+    mouse_area(positioned)
+        .on_press(Message::ClosePolarPopup)
+        .into()
+}
+
+fn angle_row<'a>(deg: f32, active: bool) -> Element<'a, Message> {
+    let check = crate::ui::icons::check_cell(active, CHECK_COLOR);
+
+    let lbl = text(angle_label(deg))
+        .size(11)
+        .color(if active { LABEL_ON } else { LABEL_OFF });
+
+    let content = row![check, lbl].spacing(6).align_y(iced::Center);
+
+    button(content)
+        .on_press(Message::SetPolarAngle(deg))
+        .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,
+};