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/io/hdf5/dynamic_hdf5_results_writer.h

@@ -5,7 +5,8 @@
 
 namespace fesa {
 
-/// @brief Writes schema-v1 HHT dynamic HDF5 results with atomic finalization.
+/// @brief Writes HHT results with atomic finalization and formulation-specific
+/// schema: v1 for full-coordinate history, v2 for reduced-coordinate history.
 class DynamicHdf5ResultsWriter final : public DynamicResultsWriter {
  public:
   /// @brief Writes a validated dynamic result file and preserves a prior final