tests: port DiscreteEllipticUtility + P2 tests; stub HDS-blocked tests

Fully ported (pure math, no HDS required):
  test_discrete_elliptic_utility.cpp  – 2 tests
    normalizeModulus: move tau into SL(2,Z) fundamental domain
  test_p2_utility.cpp                 – 3 tests
    P2 projective geometry (perpendicularBisector, pointFromLines,
    makeDirectIsometryFromFrames double vs long double precision)

New headers:
  include/discrete_elliptic_utility.hpp  – normalizeModulus
  include/p2_utility.hpp                 – P2 Euclidean geometry (templated
    on scalar type so double and long double share one implementation)

Stubs (GTEST_SKIP, blocked until HDS port – Phase 4):
  test_hyper_ideal_functional.cpp          – 5 tests (1 @Ignore in Java)
  test_hyper_ideal_hyperelliptic_utility.cpp – 3 tests
  test_spherical_functional.cpp            – 5 tests
  All use CoHDS + HalfEdgeUtils which are not yet ported to C++.

Result: 34 tests total | 21 passed | 13 skipped | 0 failed

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

code/tests/test_spherical_functional.cpp

@@ -0,0 +1,37 @@
+// Stub for de.varylab.discreteconformal.functional.SphericalFunctionalTest (Java/JUnit).
+//
+// STATUS: BLOCKED – requires HDS port (Phase 4).
+//
+// Tests evaluate gradient and Hessian of the SphericalFunctional on meshes
+// built via CoHDS + ConvexHull, and check that a regular spherical metric
+// is a critical point of the functional.  All tests require the HalfEdge
+// data structure and the functional evaluation framework in C++.
+//
+// Java tests and their status:
+//   testReducedGradient   – blocked: needs CoHDS + SphericalFunctional
+//   testReducedHessian    – blocked: needs CoHDS + SphericalFunctional
+//   testGradient          – blocked: needs CoHDS + SphericalFunctional
+//   testHessian           – blocked: needs CoHDS + SphericalFunctional
+//   testCriticalPoint     – blocked: needs CoHDS + ConvexHull + SphericalFunctional
+
+#include <gtest/gtest.h>
+
+TEST(SphericalFunctionalTest, ReducedGradient) {
+    GTEST_SKIP() << "Blocked: requires HDS port (CoHDS + SphericalFunctional)";
+}
+
+TEST(SphericalFunctionalTest, ReducedHessian) {
+    GTEST_SKIP() << "Blocked: requires HDS port (CoHDS + SphericalFunctional)";
+}
+
+TEST(SphericalFunctionalTest, Gradient) {
+    GTEST_SKIP() << "Blocked: requires HDS port (CoHDS + SphericalFunctional)";
+}
+
+TEST(SphericalFunctionalTest, Hessian) {
+    GTEST_SKIP() << "Blocked: requires HDS port (CoHDS + SphericalFunctional)";
+}
+
+TEST(SphericalFunctionalTest, CriticalPoint) {
+    GTEST_SKIP() << "Blocked: requires HDS port (CoHDS + ConvexHull + SphericalFunctional)";
+}