Select Color: review cleanups

- Split ColorEditor::view into mode_row, slider_rows, field_view,
  hex_row and hex_field; output is unchanged.
- hex_string reuses config::rgb_to_hex, and parse_hex documents why it
  stays separate (it also accepts #RGB).
- ink_is_dark uses Color::into_rgba8 instead of rounding by hand.
- Remove four translation keys the old dialog used and nothing
  references any more, from the catalog and all 22 locales.
- Eyedropper: without a main window there is no screenshot to wait for,
  so leave the eyedropper; keep the magnifier inside small windows.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_013rGmDUNr1hUf4zo1X3dak8

src/app/update/mod.rs

@@ -11039,13 +11039,16 @@ impl OpenCADStudio {
                     }
                     Some(crate::ui::color_select::Outcome::Screenshot) => {
                         use crate::ui::color_select::{eyedropper::EyedropperMsg, ColorPickerMsg};
-                        self.main_window.map_or_else(Task::none, |id| {
-                            iced::window::screenshot(id).map(|shot| {
+                        match self.main_window {
+                            Some(id) => iced::window::screenshot(id).map(|shot| {
                                 Message::ColorPicker(ColorPickerMsg::Eyedropper(
                                     EyedropperMsg::Shot(shot),
                                 ))
-                            })
-                        })
+                            }),
+                            // Nothing to capture: leave the eyedropper instead
+                            // of waiting for a screenshot that never comes.
+                            None => self.update(Message::ColorPicker(ColorPickerMsg::Cancel)),
+                        }
                     }
                     None => Task::none(),
                 }