perf(core): cache ribbon_groups() with OnceLock, avoid per-frame tree allocations

Change CadModule::ribbon_groups() from -> Vec<RibbonGroup> to -> &[RibbonGroup],
backed by a per-module OnceLock cache. The ribbon group tree is static data
(&'static str, Copy enums) that was being fully reconstructed — Vecs, String
clones, enum discriminants — on every call, including all three per-frame
call sites (view(), dropdown_overlay(), style_combo_overlay()).

- 7 built-in modules + 2 plugin templates cache via function-local OnceLock.
  Safe because each is a unit struct with exactly one instance per process
  (plugins run in isolated child processes; see PluginProcess::spawn()).
- SharedCadModule avoids the static pattern entirely, storing groups in an
  instance field (owned.rs).
- IPC runner converts &RibbonGroup -> OwnedRibbonGroup directly via new
  From<&T> impls, avoiding an intermediate clone.
- render_small/render_large and the two make_tool_row closures now borrow
  (&RibbonItem, &[ToolDef]) instead of taking ownership, so the view loop
  doesn't need to clone items to satisfy the old by-value signatures.
- Various match-ergonomics deref fixes (*id, *default, *icon, etc.) from
  the &RibbonItem pattern change.

crates/ocs_plugin_api/src/runner.rs

@@ -78,7 +78,7 @@ fn handle_host_request(
                 Ok(groups) => HostResponse::Ribbon(
                     groups
                         .ribbon_groups()
-                        .into_iter()
+                        .iter()
                         .map(OwnedRibbonGroup::from)
                         .collect(),
                 ),