feat(plugin-api): let add-ons ask for a visual style by name

Removing the binary wireframe event left add-ons with no way to set a
visual style except by spelling out a command string. Give them the
intent back, in the vocabulary everything else now speaks.

The name is carried as text rather than the render-mode type: this crate
is dependency-free by default and only pulls acadrust in behind the host
feature, which is not a weight to add to the manifest contract for one
enum. The host resolves it against the same list its ribbon, its picker
and its commands read, so an add-on can offer exactly the styles the
application does and no others. An unknown name says so and lists the
ones that exist, from that same list.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

crates/ocs_plugin_api/src/ribbon.rs

@@ -17,6 +17,15 @@ pub enum ModuleEvent {
     /// Remove all loaded models from the scene.
     #[allow(dead_code)]
     ClearModels,
+    /// Put the active viewport in a named visual style.
+    ///
+    /// The name is one of the render modes the viewport can be drawn in:
+    /// `WIREFRAME2D`, `WIREFRAME3D`, `HIDDENLINE`, `FLATSHADED`,
+    /// `GOURAUDSHADED`, `FLATSHADEDWITHEDGES`, `GOURAUDSHADEDWITHEDGES`
+    /// (case-insensitive). The host resolves it against the same list its own
+    /// ribbon and commands read, so an add-on offers exactly the styles the
+    /// application does. An unknown name is reported and nothing changes.
+    SetVisualStyle(String),
     /// Toggle the layer manager panel.
     ToggleLayers,
     /// Ask the host to open a native file picker. On selection the host