feat(cgal): propagate Newton status + conditioning diagnostics into CGAL results

Follow-up to S2: surface the new NewtonResult diagnostics through the public
CGAL result types so callers of the high-level API see them too.

- Add `CGAL::Newton_status` (alias of conformallab::NewtonStatus) and three
  fields — `status`, `sparse_qr_fallback_used`, `min_ldlt_pivot` — to
  Conformal_map_result, Hyper_ideal_map_result and Circle_packing_result.
  (sparse_qr_fallback_used already existed on Conformal_map_result but was never
  populated; it is now wired through.)
- Map them from NewtonResult at all five entry points (euclidean / spherical /
  hyper_ideal / inversive_distance / cp_euclidean).
- Test: SingleTriangleConverges now asserts status == Converged and the
  diagnostics propagate.

Additive only — existing `converged`/`iterations`/`gradient_norm` semantics
unchanged. 301/301 CGAL tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

code/tests/cgal/test_cgal_traits_mvp.cpp

@@ -111,6 +111,11 @@ TEST(CGALDiscreteConformalMap, SingleTriangleConverges)
     EXPECT_GE(result.iterations, 0);
     EXPECT_EQ(result.u_per_vertex.size(), num_vertices(mesh));
 
+    // I1/N7 propagated through the CGAL layer: status enum + diagnostics.
+    EXPECT_EQ(result.status, CGAL::Newton_status::Converged);
+    EXPECT_FALSE(result.sparse_qr_fallback_used);   // pinned vertex → no gauge mode
+    EXPECT_GE(result.min_ldlt_pivot, 0.0);
+
     // With the default flat-disc target curvature and the first vertex pinned,
     // the natural-theta equilibrium is at u = 0 — Newton should accept x0=0.
     for (double u : result.u_per_vertex)