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>

code/include/CGAL/Discrete_conformal_map.h

@@ -449,8 +449,11 @@ struct Hyper_ideal_map_result
     /// Edge DOFs `a_e` (length = num_edges(mesh); pinned edges = 0).
     std::vector<FT> a_per_edge;
 
+    /// Newton iterations actually performed (≤ `max_iterations`).
     int  iterations    = 0;
+    /// Final infinity-norm of the gradient (Newton stopping criterion).
     FT   gradient_norm = FT(0);
+    /// `true` iff `gradient_norm < gradient_tolerance` at exit.
     bool converged     = false;
 };