Share the colour editor, add an eyedropper, use library code

- ColorEditor: the HSB / RGB / field editor and hex box, now shared by
  the Select Color panel and the Options background swatches. Those
  swatches open the panel without tabs or index colours, which removes
  the iced_aw color_picker feature and the BgPicker messages.
- Sliders are iced's built-in slider and vertical_slider over a
  gradient container; the custom GradientSlider widget is gone.
- Nearest index colour comes from opencadcodec's aci_table::nearest_aci.
- Eyedropper: a pipette at the right of the mode row hides the panel,
  captures the window with iced's screenshot task and shows an 11x11
  magnifier beside a crosshair; a click picks the pixel, Esc backs out.
  Not offered on the web build.
- The hex box applies six-digit values while typing.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013rGmDUNr1hUf4zo1X3dak8

src/ui/window/options.rs

@@ -157,22 +157,18 @@ impl<T> fmt::Display for Labelled<T> {
     }
 }
 
-/// A background swatch that opens the colour wheel when clicked.
+/// A background swatch that opens the colour picker when clicked.
 ///
-/// The wheel sits alongside the hex field rather than replacing it: typing
+/// The picker sits alongside the hex field rather than replacing it: typing
 /// `#1E1E1E` stays the fastest way to reproduce an exact colour, while the
-/// wheel is for choosing one by eye.
-fn bg_swatch_picker<'a>(
-    target: crate::app::BgTarget,
-    rgb: [u8; 3],
-    open: Option<crate::app::BgTarget>,
-) -> Element<'a, Message> {
-    let colour = iced::Color::from_rgb8(rgb[0], rgb[1], rgb[2]);
+/// picker is for choosing one by eye.
+fn bg_swatch_picker<'a>(target: crate::app::BgTarget, rgb: [u8; 3]) -> Element<'a, Message> {
+    let [r, g, b] = rgb;
     let swatch = container(Space::new())
         .width(28)
         .height(22)
         .style(move |theme: &Theme| container::Style {
-            background: Some(Background::Color(colour)),
+            background: Some(Background::Color(iced::Color::from_rgb8(r, g, b))),
             border: Border {
                 color: theme.palette().background.strong.color,
                 width: 1.0,
@@ -180,18 +176,14 @@ fn bg_swatch_picker<'a>(
             },
             ..Default::default()
         });
-    let underlay = button(swatch)
-        .on_press(Message::BgPickerOpen(target))
+    button(swatch)
+        .on_press(Message::OpenColorWindow(
+            crate::app::ColorPickTarget::Background(target),
+            codec::types::Color::Rgb { r, g, b },
+        ))
         .padding(0)
-        .style(button::text);
-    iced_aw::ColorPicker::new(
-        open == Some(target),
-        colour,
-        underlay,
-        Message::BgPickerCancel,
-        Message::BgPickerSubmit,
-    )
-    .into()
+        .style(button::text)
+        .into()
 }
 
 #[allow(clippy::too_many_arguments)]
@@ -227,7 +219,6 @@ pub fn view_window<'a>(
     model_bg_input: &'a str,
     paper_bg_input: &'a str,
     desk_bg_input: &'a str,
-    bg_picker: Option<crate::app::BgTarget>,
     dirty: bool,
     close_confirm: bool,
     sizing: crate::ui::modal::ModalSizing,
@@ -742,7 +733,7 @@ pub fn view_window<'a>(
         display = display.push(Space::new().height(10)).push(
             row![
                 text(crate::t!("Model background")).size(12).width(140),
-                bg_swatch_picker(crate::app::BgTarget::Model, model_bg_rgb, bg_picker),
+                bg_swatch_picker(crate::app::BgTarget::Model, model_bg_rgb),
                 text_input("#RRGGBB", model_bg_input)
                     .on_input(Message::ModelSpaceBgChanged)
                     .width(150),
@@ -755,7 +746,7 @@ pub fn view_window<'a>(
     display = display.push(Space::new().height(10)).push(
         row![
             text(crate::t!("Paper background")).size(12).width(140),
-            bg_swatch_picker(crate::app::BgTarget::Paper, paper_bg_rgb, bg_picker),
+            bg_swatch_picker(crate::app::BgTarget::Paper, paper_bg_rgb),
             text_input("#RRGGBB", paper_bg_input)
                 .on_input(Message::PaperSpaceBgChanged)
                 .width(150),
@@ -767,7 +758,7 @@ pub fn view_window<'a>(
     display = display.push(Space::new().height(10)).push(
         row![
             text(crate::t!("Desk surround")).size(12).width(140),
-            bg_swatch_picker(crate::app::BgTarget::Desk, desk_bg_rgb, bg_picker),
+            bg_swatch_picker(crate::app::BgTarget::Desk, desk_bg_rgb),
             text_input("#RRGGBB", desk_bg_input)
                 .on_input(Message::DeskSpaceBgChanged)
                 .width(150),