feat(view): add visual style previews

- preview render modes on hover without committing
- distinguish 2D and 3D wireframe fill and depth behavior

Refs #483

src/app/update/mod.rs

@@ -1191,7 +1191,30 @@ impl OpenCADStudio {
                 Task::done(Message::SetRenderMode(mode))
             }
 
-            Message::SetRenderMode(mode) => self.on_set_render_mode(mode),
+            Message::SetRenderMode(mode) => {
+                self.render_mode_menu_open = false;
+                self.render_mode_preview = None;
+                self.on_set_render_mode(mode)
+            }
+
+            Message::ToggleRenderModeMenu(mode) => {
+                self.render_mode_menu_open = !self.render_mode_menu_open;
+                self.render_mode_preview = self.render_mode_menu_open.then_some(mode);
+                Task::none()
+            }
+
+            Message::DismissRenderModeMenu => {
+                self.render_mode_menu_open = false;
+                self.render_mode_preview = None;
+                Task::none()
+            }
+
+            Message::PreviewRenderMode(mode) => {
+                if self.render_mode_menu_open {
+                    self.render_mode_preview = Some(mode);
+                }
+                Task::none()
+            }
 
             Message::SetProjection(ortho) => {
                 use crate::scene::Projection;

src/app/update/viewport.rs

@@ -1757,6 +1757,7 @@ impl OpenCADStudio {
                             world_width: 0.0,
                             depth_override: None,
                             fill_is_3d: false,
+                            fill_is_2d_solid: false,
                             pick_tris: Vec::new(),
                             pick_tris_low: Vec::new(),
                             dash_from_start: false,