1D elements I: trusses (rod2, rod3), point masses, rotary inertia, springs and dashpots (#38)

* Model, fem and decks: point masses, rotary inertia, springs, dashpots and rod3 trusses

Model: PointMass and Spring definitions (spring | dashpot; to ground or
two-point; along a degree of freedom, a vector or the line of the ends) on a
set or reference point, resolved per node; ElementKind::Rod3. fem: rod2/rod3
truss kernel on Basis::Line2/Line3 declaring ElementDofs (translations).
Decks: Abaqus T3D3, MASS, ROTARYI, SPRING1/2/A, DASHPOT1/2/A; Nastran CONM1,
CELAS2, CDAMP2; LS-DYNA ELEMENT_MASS/INERTIA and ELEMENT_DISCRETE; what a
format cannot take is reported. Commands model.mass.* and model.spring.*.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* Implicit solver: trusses, point masses, rotary inertia and springs on the DofLayout

Trusses declare their translations like solids; point masses, inertia and
springs ask the layout for the kinds they need at their nodes (translations,
rotations), and reference points they use get six degrees of freedom. The
matrix pattern takes rows for those points; dashpots are ignored with a
warning. Existing results are bit-identical (hash-checked).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* Explicit solver: trusses, point masses, springs and dashpots on the node-major layout

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* docs: fem.md on trusses and discrete elements in the layout; regenerate features.md

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* docs: trusses in plane models and corotational explicit trusses

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

---------

Co-authored-by: jyviko <2501648+jyviko@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/catalogue.rs

@@ -306,8 +306,22 @@ pub static CATALOGUE: &[Capability] = &[
     soon("interaction.contact.find", "Find Contacts", Interactions, "Contact", "M7", "Detect contact pairs automatically"),
     soon("interaction.rigid_wall", "Rigid Wall", Interactions, "Contact", "M10", "Rigid walls for explicit dynamics"),
     soon("interaction.bolt", "Bolt Load", Interactions, "Connectors", "M7", "Bolt pretension"),
-    soon("interaction.spring", "Spring", Interactions, "Connectors", "M7", "Springs and dashpots"),
-    soon("interaction.mass", "Point Mass", Interactions, "Connectors", "M7", "Point masses and inertia"),
+    ready_more(
+        "model.spring.create",
+        "Spring",
+        Interactions,
+        "Connectors",
+        "Spring or dashpot to the ground or between two points, along a direction or their line",
+        &["model.spring.edit", "model.spring.delete"],
+    ),
+    ready_more(
+        "model.mass.create",
+        "Point Mass",
+        Interactions,
+        "Connectors",
+        "Point mass and rotary inertia at nodes or a reference point",
+        &["model.mass.edit", "model.mass.delete"],
+    ),
     soon("interaction.connector", "Connector", Interactions, "Connectors", "M7", "Connector elements between points"),
     soon("interaction.fsi", "FSI Interface", Interactions, "Coupled", "M13", "The fluid–structure interface"),
     // ---- Solve ----