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Remove accidental dead code (unused imports, the superseded paste tool()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/app/style_ops.rs

@@ -47,7 +47,7 @@ impl OpenCADStudio {
     /// sorted by name so the `HashMap` backing them renders stably).
     pub(super) fn style_names(&self, kind: StyleKind) -> Vec<String> {
         let doc = &self.tabs[self.active_tab].scene.document;
-        let mut from_objects = |pick: fn(&ObjectType) -> Option<&str>| -> Vec<String> {
+        let from_objects = |pick: fn(&ObjectType) -> Option<&str>| -> Vec<String> {
             let mut v: Vec<String> = doc
                 .objects
                 .values()