docs(doxygen): 100% public-API coverage (228 → 0 undocumented)

Completes the work begun in the previous commit on this branch.  Every
public symbol under code/include/ now carries a brief Doxygen comment
(0 undocumented per scripts/doxygen-coverage.sh, with the `detail::`
implementation namespaces excluded as before).

Trajectory on this branch:
  start (after Doxyfile fix):  24.0 %  (165 / 437 in the no-detail set
                                       was 105 / 437 when detail counted)
  after PR #17 base commit  :  42.4 %  (165 / 396)
  this commit               : 100.0 %  (396 / 396)

Files touched (all .hpp / .h headers under code/include/):
  * cgal/Conformal_map_traits.h
  * clausen.hpp, conformal_mesh.hpp, constants.hpp (already docd)
  * cp_euclidean_functional.hpp, cut_graph.hpp, discrete_elliptic_utility.hpp
  * euclidean_functional.hpp, euclidean_geometry.hpp, euclidean_hessian.hpp
  * fundamental_domain.hpp, gauss_bonnet.hpp
  * hyper_ideal_{functional,geometry,hessian,utility,visualization_utility}.hpp
  * inversive_distance_functional.hpp, layout.hpp
  * matrix_utility.hpp, mesh_builder.hpp, mesh_io.hpp
  * newton_solver.hpp, p2_utility.hpp, period_matrix.hpp, projective_math.hpp
  * serialization.hpp, spherical_functional.hpp, spherical_geometry.hpp
  * spherical_hessian.hpp, viewer_utils.h

CI:
.gitea/workflows/doxygen-pages.yml now enforces
`scripts/doxygen-coverage.sh --threshold 100`, so any future regression
(a new public function landed without a `///` brief) fails the build
before the Doxygen HTML is published to Codeberg Pages.

Doxygen warnings remain at 0.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

code/include/inversive_distance_functional.hpp

@@ -76,12 +76,17 @@ namespace conformallab {
 
 // ── Property-map type aliases ────────────────────────────────────────────────
 
+/// Property map vertex → `int`    for the Inversive-Distance functional.
 using IDVMapI = ConformalMesh::Property_map<Vertex_index, int>;
+/// Property map vertex → `double` for the Inversive-Distance functional.
 using IDVMapD = ConformalMesh::Property_map<Vertex_index, double>;
+/// Property map edge   → `double` for the Inversive-Distance functional.
 using IDEMapD = ConformalMesh::Property_map<Edge_index, double>;
 
 // ── Persistent map bundle ─────────────────────────────────────────────────────
 
+/// Bundle of the four property maps consumed by the Inversive-Distance
+/// circle-packing functional (Luo 2004 / Bowers-Stephenson 2004).
 struct InversiveDistanceMaps {
     IDVMapI v_idx;       ///< DOF index per vertex (−1 = pinned / u_v = 0)
     IDVMapD theta_v;     ///< target cone angle Θ_v   (default 2π)
@@ -225,12 +230,8 @@ inline double edge_length_squared(double u_i, double u_j, double I_ij) noexcept
 
 } // namespace id_detail
 
-// ── Gradient ──────────────────────────────────────────────────────────────────
-//
-// G_v = Θ_v − Σ_{f ∋ v} α_v(f)
-//
-// Halfedge convention (identical to euclidean_functional.hpp):
-//   h_alpha[h] = corner angle OPPOSITE to the edge of halfedge h in its face.
+/// Inversive-Distance gradient `G_v = Θ_v − Σ_faces α_v(face)`.  Same
+/// half-edge corner-angle storage convention as `euclidean_gradient`.
 inline std::vector<double> inversive_distance_gradient(
     const ConformalMesh&             mesh,
     const std::vector<double>&       x,
@@ -291,9 +292,8 @@ inline std::vector<double> inversive_distance_gradient(
     return G;
 }
 
-// ── Energy via Gauss-Legendre path integral ─────────────────────────────────
-//
-// E(u) = ∫₀¹ ⟨G(tu), u⟩ dt   (10-point GL, identical constants to euclidean_functional)
+/// Inversive-Distance energy `E(u) = ∫₀¹ ⟨G(t·u), u⟩ dt`, evaluated
+/// with 10-point Gauss-Legendre (constants shared with `euclidean_energy`).
 inline double inversive_distance_energy(
     const ConformalMesh&             mesh,
     const std::vector<double>&       x,
@@ -329,7 +329,7 @@ inline double inversive_distance_energy(
     return E;
 }
 
-// ── Finite-difference gradient check ─────────────────────────────────────────
+/// FD gradient check for the Inversive-Distance functional (central diff).
 inline bool gradient_check_inversive_distance(
     const ConformalMesh&             mesh,
     const std::vector<double>&       x,
@@ -358,7 +358,8 @@ inline bool gradient_check_inversive_distance(
     return true;
 }
 
-// ── Newton equilibrium check: gradient vanishes at converged u ──────────────
+/// Newton equilibrium check: returns `true` iff the gradient at `x`
+/// is below `tol` in infinity norm (Σ adj-face angles equal Θ_v).
 inline bool is_inversive_distance_equilibrium(
     const ConformalMesh&             mesh,
     const std::vector<double>&       x,