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.

src/fesa/CMakeLists.txt

@@ -8,6 +8,8 @@ add_library(
     analysis/hht_time_integration.cpp
     analysis/hht_dynamic_algebra.cpp
     analysis/hht_dynamic_assembly.cpp
+    analysis/hht_reduced_operators.cpp
+    analysis/hht_reduced_procedure.cpp
     analysis/hht_dynamic_procedure.cpp
     analysis/linear_frequency_procedure.cpp
     analysis/linear_static_analysis.cpp