refactor(api): consistent naming for spherical + hyper-ideal helpers (A1–A3)

Standardize the low-level free-function API on <verb>_<geom>_<rest>,
matching the already-consistent setup_<geom>_maps. Old names kept as
[[deprecated]] inline aliases for one release; all internal call sites
migrated.

Renames:
  assign_vertex_dof_indices      -> assign_spherical_vertex_dof_indices
  assign_all_spherical_dof_indices -> assign_spherical_all_dof_indices
  assign_all_dof_indices         -> assign_hyper_ideal_all_dof_indices
  compute_lambda0_from_mesh      -> compute_spherical_lambda0_from_mesh
  gradient_check                 -> gradient_check_hyper_ideal

A4/A5 (public CGAL API) intentionally deferred pending the license/
provenance decision (see CGAL submission audit G0/G1).

Verified: 277/277 CGAL tests pass, no deprecation warnings.

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

code/tests/cgal/test_lawson_hyperideal.cpp

@@ -160,7 +160,7 @@ TEST(LawsonHyperIdeal, ConvergenceGoldenVector_JavaXVal)
     ConformalMesh m = make_lawson_square_tiled(&original);
 
     HyperIdealMaps maps = setup_hyper_ideal_maps(m);     // Θ_v=2π, θ_e=π
-    const int n = assign_all_dof_indices(m, maps);       // all vertices + edges
+    const int n = assign_hyper_ideal_all_dof_indices(m, maps);       // all vertices + edges
     ASSERT_EQ(n, 4 + 18);                                // 4 b + 18 a = 22 DOFs
 
     // θ_e = π/2 for the 12 original edges; the 6 diagonals keep the default π.