Redesign Select Color panel: index and true color tabs

Replace the old index page and the iced_aw ColorPicker popup with one
Select Color panel:

- Index Color tab: standard colors, ACI 10-249 grid, grays; arrow keys
  move through the palette.
- True Color tab: HSB, RGB and gradient-field modes built on two new
  widgets (GradientSlider, ColorArea) and iced_aw NumberInput boxes,
  an editable hex field and a nearest/exact index color button.
- Current/New swatch: clicking Current reverts. A mixed selection opens
  on the color of the most recently drawn object with *VARIES* on top.
- Color field accepts an index, a color name, r,g,b or hex.
- Enter confirms, Esc cancels, other keys stay in the panel.
- New labels translated in all 22 locales.

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

locales/ru-RU/opencadstudio.ftl

@@ -1330,6 +1330,9 @@ common =
     .index-color = { common.color } (ACI)
     .true-color = { common.color } (RGB)
     .standard-colors = { common.standard } · { common.color }
+    .color-hex = Hex
+    .nearest-index-color = Ближайший индекс
+    .exact-index-match = Точное совпадение с индексом
     .cad-color-index-aci-10-249 = Индекс цвета ACI 10–249
     .color-family-shade-intensity = { common.color-family } → · { common.shade } / { properties.intensity } ↓
     .grayscale-250-255 = { common.grayscale } 250–255