results: results.xy, a quantity against the load factor, time or mode (#94)

A nodal field at a node per frame (nonlinear static displacements from
load factor 0, explicit frames, heat temperatures) or per mode, the
explicit energies and histories, history nodes, and the frequencies or
buckling load factors; capped at 100000 points with `every`; stale
results refused; `path` writes a two-column CSV. XY Plot is ready.

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

crates/engine/src/catalogue.rs

@@ -627,7 +627,7 @@ pub static CATALOGUE: &[Capability] = &[
     ),
     ready_more("results.reactions", "Reactions", Results, "Query", "Reaction force and moment sums per set", &["results.export.csv"]),
     soon("results.free_body", "Free Body", Results, "Query", "M9", "Free-body forces across a cut"),
-    soon("results.xy", "XY Plot", Results, "Plots", "M9", "Plot a quantity against time or another"),
+    ready("results.xy", "XY Plot", Results, "Plots", "Plot a quantity against the load factor, time or mode"),
     soon("results.path", "Path Plot", Results, "Plots", "M9", "Plot a quantity along a path"),
     soon("results.cut", "Cut", Results, "Plots", "M9", "Section cuts through the model"),
     soon("results.display_group", "Display Group", Results, "Plots", "M9", "Show and hide parts of the model"),