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Remove accidental dead code (unused imports, the superseded paste tool()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 <[email protected]>

src/command/mod.rs

@@ -379,6 +379,7 @@ pub enum DynAnchor {
 pub struct DynFieldSpec {
     pub role: DynRole,
     /// Label override; `None` uses the role's default label.
+    #[allow(dead_code)] // dyn-spec framework field; not yet consumed
     pub label: Option<&'static str>,
 }