feat(select): orange hover / blue selection highlight for all objects

Solids (meshes) now tint on rollover and selection: hover washes orange,
selection washes blue, with selection winning when both apply. Meshes
re-upload their tint when the highlight set changes, and the rollover pick
now also hits shaded solid bodies and hatches (mirroring the click-select
order: wire → hatch → block hatch → solid).

Wires get the same scheme: the selection xray overlay recolours selected
entities blue and the hovered entity orange (previously both blue). Drops
the now-unused highlight_handles union helper and its cache.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/scene/model/wire_model.rs

@@ -79,6 +79,8 @@ impl WireModel {
     pub const WHITE: [f32; 4] = [1.00, 1.00, 1.00, 1.0];
     pub const CYAN: [f32; 4] = [0.25, 0.85, 1.00, 1.0];
     pub const SELECTED: [f32; 4] = [0.15, 0.55, 1.00, 1.0];
+    /// Rollover (hover) highlight — orange, distinct from the blue selection.
+    pub const HOVER: [f32; 4] = [0.95, 0.55, 0.10, 1.0];
     /// Sentinel AABB that never rejects any snap query.
     pub const UNBOUNDED_AABB: [f32; 4] = [
         f32::NEG_INFINITY,