docs(doxygen): fix critical extraction bug; baseline 24% → 42% on public API

ROOT CAUSE FIX
The Doxyfile EXCLUDE_PATTERNS line contained `*/* 2.hpp` (note the
space — a stray glob from macOS-style "foo 2.hpp" duplicate files).
That pattern was silently matching ALL .hpp / .h files, so Doxygen was
indexing nothing under code/include/.  The pre-existing 556 KB of HTML
output was effectively documenting only README.md, CLAUDE.md and a
small stub for std:: — not the C++ API at all.

After fixing the pattern (and properly escaping the space-prefixed
"foo 2.hpp / foo 2.h" macOS-dup patterns), Doxygen now extracts 141
compounds and emits 248 HTML pages from the public headers.

WHAT THIS PR ADDS
1. Doxyfile fix: correct EXCLUDE_PATTERNS; add GENERATE_XML for the
   coverage measurement script; add MathJax for `$$...$$` math in
   markdown; add the missing CGAL `\cgalParamNBegin/End/Description/
   Default/...` aliases so CGAL-style param blocks render correctly.

2. New headers:
   - code/include/CGAL/Conformal_map/doxygen_groups.h
     defines `PkgConformalMap{,Ref,Concepts,NamedParameters}`,
     resolving 17 prior "non-existing group" warnings.
   - code/include/CGAL/Conformal_map/doxygen_namespaces.h
     gives every namespace under `CGAL::` and `conformallab::` a
     brief description.

3. New tool: scripts/doxygen-coverage.sh
   Parses the XML output and reports % of public symbols (excluding
   the `detail::` implementation namespaces by default) that have a
   non-empty brief/detailed description.  Supports `--list-undoc`
   and `--threshold N` for CI integration.

4. Substantial docstring additions to the public CGAL headers:
   `Conformal_map_traits.h`, `Discrete_circle_packing.h`,
   `Discrete_inversive_distance.h`, `conformal_mesh.hpp`,
   `Discrete_conformal_map.h` (Hyper_ideal_map_result fields).

5. Markdown housekeeping that the strict-warning Doxygen run surfaced:
   tests.md (escape literal `#` in table cell),
   locked-vs-flexible.md (broken section anchor),
   overall_pipeline.md (replace `$$LaTeX$$` with inline-unicode math).

CURRENT NUMBERS

  before:  ~24%  documented (public API; the prior "87%" claim was
                 based on the broken extraction)
  after:    42%  documented   (165 of 396 public symbols)
  warnings: 0   (was 27 spurious + a flood of bogus undocumented
                  warnings hidden by the buggy EXCLUDE pattern)

NEXT (in a follow-up commit on this branch)
The remaining 231 public symbols (mostly in `layout.hpp`,
`hyper_ideal_functional.hpp`, `spherical_functional.hpp`, the per-mode
functional/Hessian files) can be brought to ~100% with another pass of
short `///` brief descriptions.  The coverage script is the gate; CI
can begin enforcing `--threshold 95` once the next pass lands.

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

doc/architecture/overall_pipeline.md

@@ -150,7 +150,7 @@ maps.theta_v[v] = M_PI / 3;          // 60° cone singularity
 
 Before solving, the prescribed angles must satisfy:
 
-$$\sum_{v} (2\pi - \Theta_v) = 2\pi \cdot \chi(M)$$
+> ∑ᵥ (2π − Θᵥ) = 2π · χ(M)
 
 ```cpp
 check_gauss_bonnet(mesh, maps);         // throws if violated
@@ -283,7 +283,7 @@ Both `uv` and `halfedge_uv` are transformed identically.
 From the two holonomy translations ω₁, ω₂ ∈ ℂ read off from the cut graph,
 the conformal type of a flat torus is the SL(2,ℤ)-orbit of:
 
-$$\tau = \omega_2 / \omega_1 \in \mathbb{H}$$
+> τ = ω₂ / ω₁ ∈ ℍ
 
 ```cpp
 PeriodData pd = compute_period_matrix(hol);