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/ui/tablestyle.rs

@@ -140,6 +140,7 @@ pub fn view_window<'a>(
                     value: crate::ui::color_select::color_to_aci_string(c),
                 },
                 Message::TableColorMore(row, field),
+                Message::OpenColorWindow(crate::app::ColorPickTarget::Table(row, field)),
             );
             row![text(label).size(11).color(DIM).width(150), selector]
                 .spacing(8)