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/include/CGAL/Discrete_conformal_map.h

@@ -345,7 +345,7 @@ auto discrete_conformal_map_spherical(
     Conformal_map_result<FT> result;
 
     auto maps = ::conformallab::setup_spherical_maps(mesh);
-    ::conformallab::compute_lambda0_from_mesh(mesh, maps);
+    ::conformallab::compute_spherical_lambda0_from_mesh(mesh, maps);
 
     auto theta_param = parameters::get_parameter(
         np, Conformal_map::internal_np::vertex_curvature_map);
@@ -499,7 +499,7 @@ auto discrete_conformal_map_hyper_ideal(
             maps.theta_v[v] = get(theta_param, v);
     }
 
-    const int n = ::conformallab::assign_all_dof_indices(mesh, maps);
+    const int n = ::conformallab::assign_hyper_ideal_all_dof_indices(mesh, maps);
 
     const FT  tol      = parameters::choose_parameter(
         parameters::get_parameter(np, Conformal_map::internal_np::gradient_tolerance),