chore: clear compiler warnings

Remove accidental dead code (unused imports, the superseded paste tool()
helper, a never-read TORIENT handles field, a duplicate let binding, an
unneeded mut) and mark intentional-but-unwired scaffolding with
allow(dead_code): the web-only save_to_bytes, the plugin loadable() probe,
the planned PICK_HIGHLIGHT colours, the DynFieldSpec label, and the layout
ribbon helpers. Native build is now warning-clean apart from the upstream
nom/quick-xml future-incompat notices.

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

src/ui/color_select.rs

@@ -407,7 +407,7 @@ impl<'a> Widget<Message, Theme, Renderer> for Floating<'a> {
         &'b mut self,
         tree: &'b mut widget::Tree,
         layout: Layout<'b>,
-        renderer: &Renderer,
+        _renderer: &Renderer,
         _viewport: &Rectangle,
         translation: Vector,
     ) -> Option<overlay::Element<'b, Message, Theme, Renderer>> {