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 <[email protected]>

src/app/view/mod.rs

@@ -1253,6 +1253,7 @@ impl OpenCADStudio {
                         self.ortho_mode,
                         self.polar_mode,
                         self.polar_increment_deg,
+                        self.polar_popup_open,
                         self.dyn_input,
                         self.snapper.otrack_enabled,
                         tab.scene.layout_names(),
@@ -1320,6 +1321,17 @@ impl OpenCADStudio {
             iced::widget::Space::new().width(0).height(0).into()
         };
 
+        let polar_layer: Element<'_, Message> = if self.polar_popup_open {
+            crate::ui::popup::polar_popup::polar_popup_overlay(
+                self.polar_increment_deg,
+                &self.polar_custom_input,
+                sb_pill(crate::ui::statusbar::SB_POLAR_ID),
+                win,
+            )
+        } else {
+            iced::widget::Space::new().width(0).height(0).into()
+        };
+
         let statusbar_menu_layer: Element<'_, Message> = if self.statusbar_menu_open {
             crate::ui::statusbar::statusbar_menu::statusbar_menu_overlay(
                 &self.statusbar_config,
@@ -1412,6 +1424,7 @@ impl OpenCADStudio {
             main_ui,
             snap_layer,
             scale_layer,
+            polar_layer,
             statusbar_menu_layer,
             layout_list_layer,
             units_layer,