engine: contact output of nonlinear static steps

solve.nonlinear summarises each contact (normal force, largest pressure, closed nodes, deepest
penetration, augmentations), solve.probe gives a secondary node's pressure, gap and status per
contact, and the results display draws contact_pressure, contact_gap and contact_status. The
contact commands, the catalogue and the model docs say what nonlinear static steps do with a
pair.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/engine/src/catalogue.rs

@@ -428,7 +428,7 @@ pub static CATALOGUE: &[Capability] = &[
         "Contact Pair",
         Interactions,
         "Contact",
-        "Contact between two surfaces, with friction (explicit dynamics)",
+        "Contact between two surfaces: with friction in explicit dynamics, frictionless mortar contact in nonlinear static steps",
         &["interaction.contact.edit", "interaction.contact.delete"],
     ),
     ready(