feat: adopt lumped mass and reduced-coordinate shell HHT

Integrate Hex8 mass verification and fixed-null-basis shell dynamics with numerical and physics handoff evidence. Preserve interrupted reference and full-validation status; full integration validation is deferred until after performance optimization.

include/fesa/elements/nonlinear_mitc4_inertia.h

@@ -38,7 +38,7 @@ struct DynamicRotationKinematics {
     const Vector3& phi, const Vector3& initial_director,
     const Vector3& velocity, const Vector3& acceleration);
 
-/// @brief Stores the consistent kinetic-inertia quantities at one trial.
+/// @brief Stores the nodal lumped kinetic-inertia quantities at one trial.
 struct NonlinearMitc4InertiaEvaluation {
   Matrix mass;
   Matrix position_tangent;
@@ -55,12 +55,12 @@ struct NonlinearMitc4InertiaEvaluation {
   double angular_momentum_rate_scale = 0.0;
 };
 
-/// @brief Evaluates finite-rotation consistent inertia for one MITC4 shell.
+/// @brief Evaluates finite-rotation nodal lumped inertia for one MITC4 shell.
 /// @note This object owns immutable reference geometry only, never analysis
 /// trial state.
 class NonlinearMitc4Inertia {
  public:
-  /// @brief Creates a checked consistent kinetic-mass evaluator.
+  /// @brief Creates a checked nodal lumped kinetic-mass evaluator.
   /// @param nodes Four non-owning nodes in source order.
   /// @param initial_frames Fixed proper node frames in source order.
   /// @param section Centered shell section with positive thickness.
@@ -74,7 +74,7 @@ class NonlinearMitc4Inertia {
       const ShellSection& section, const LinearElasticMaterial& material,
       double density);
 
-  /// @brief Evaluates physical consistent inertia at a complete trial.
+  /// @brief Evaluates physical nodal lumped inertia at a complete trial.
   /// @param trial Fixed-global translation and rotation coordinates.
   /// @param velocity24 Fixed-chart generalized physical velocity.
   /// @param physical_acceleration24 Fixed-chart generalized physical