feat: add eigen2 frequency pipeline and fail-closed validation

Implement MITC4 mass, constrained whitening, MKL FEAST, modal HDF5, and deterministic Value comparison. MSVC Debug builds; 394 of 395 tests pass. Original-model all-c residual and the documented S3 static contract conflict remain unresolved; this is an implementation checkpoint, not feature acceptance.

src/fesa/analysis/linear_static_procedure.cpp

@@ -26,6 +26,16 @@ LinearStaticProcedureExecutor::LinearStaticProcedureExecutor(
 
 Result<LinearStaticExecutionResult> LinearStaticProcedureExecutor::Execute(
     const Domain& domain) const {
+  if (domain.Frequency() != nullptr) {
+    return Result<LinearStaticExecutionResult>::Failure(Status::Failure(
+        FailureCategory::kModel,
+        {{Severity::kError,
+          "invalid-analysis-procedure",
+          domain.Frequency()->frequency_location,
+          "FREQUENCY",
+          {},
+          "Linear-static execution cannot consume a frequency step."}}));
+  }
   Result<AnalysisModel> model = AnalysisModel::Create(domain);
   if (!model.HasValue()) {
     return Result<LinearStaticExecutionResult>::Failure(model.GetStatus());