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/scene/mod.rs

@@ -1649,6 +1649,9 @@ pub struct Scene {
     /// constants. `[depth, half]` retains a fixed child sub-range for block
     /// composition. Full sort/layout/block changes rebuild the labels.
     draw_depth_cache: RefCell<Option<DrawDepthCache>>,
+    /// Shared empty map for 3-D wireframe, where true depth wins instead of
+    /// the entity submission order used by the optimized 2-D style.
+    no_draw_depths: Arc<HashMap<u64, [f32; 2]>>,
     /// Cached hatch fill models, keyed by target block and geometry_epoch. View culling
     /// is handled at draw time via `hatch_skip_flags` in the pipeline,
     /// not at build time — that lets the GPU buffer stay stable across
@@ -1960,6 +1963,7 @@ impl Scene {
             interaction_handle_index_cache: RefCell::new(None),
             sort_cache: RefCell::new(None),
             draw_depth_cache: RefCell::new(None),
+            no_draw_depths: Arc::new(HashMap::default()),
             hatch_cache: RefCell::new(HashMap::default()),
             wipeout_cache: RefCell::new(HashMap::default()),
             image_cache: RefCell::new(HashMap::default()),