Environment Map Analysis: the model's faces as a mirror reflecting a studio (sky, horizon band, floor with light streaks, two light panels); toggles like the other surface analyses

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

crates/engine/src/lib.rs

@@ -176,6 +176,8 @@ pub enum SurfaceAnalysis {
     Draft { pull: Vec3, angle: f64 },
     /// Colour by curvature: blue flat, through green, to red at 1 / `radius`.
     Curvature { radius: f64 },
+    /// Mirror finish reflecting a studio (sky, horizon, floor, light panels).
+    Environment,
 }
 
 const MAX_UNDO: usize = 200;