feat(ui): move full ACI palette to a separate "Select Color" window (#94)

The colour selector popup now lists only the named colours (ByLayer,
ByBlock, ACI 1-9) plus a "More…" entry. "More…" opens a standalone
"Select Color" window with the full 256-colour grid; picking there applies
to the originating field (dimension/multileader/table style) and closes
the window. Routed via a ColorPickTarget so one window serves every field.

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

src/app/view.rs

@@ -465,6 +465,9 @@ impl OpenCADStudio {
                 &self.style_rename_buf,
             );
         }
+        if Some(window_id) == self.color_pick_window {
+            return crate::ui::color_select::color_grid_window(Message::ColorWindowPick);
+        }
         if Some(window_id) == self.shortcuts_window {
             return crate::ui::shortcuts::view_window(&self.shortcut_overrides);
         }