fix(citations): correct Kolpakov-Mednykh misattribution → Springborn 2008

arXiv:math/0603097 is Springborn 2008 ("A variational principle for weighted
Delaunay triangulations and hyperideal polyhedra"), not a Kolpakov-Mednykh paper.
The author pair Kolpakov & Mednykh has no joint publication from 2006; their
earliest collaboration is arXiv:1008.0312 (2010, on torus knots, unrelated).

The wrong author name was introduced during the Java→C++ port — the Java source
correctly links to math/0603097 without naming the authors; whoever ported it
invented "Kolpakov-Mednykh". The S1 citation audit (2026-05-31) then cemented
the error by adding the incorrect row to references.md.

Files corrected (7):
- code/include/hyper_ideal_utility.hpp
- code/include/hyper_ideal_functional.hpp
- code/tests/cgal/test_hyper_ideal_functional.cpp
- doc/math/references.md
- doc/roadmap/research-track.md
- doc/architecture/project-structure.md
- doc/api/tests.md

Also:
- doc/reviewer/math-derivation-citation-audit-2026-05-31.md: M1 post-correction noted
- doc/reviewer/finding-orchestration.md: lesson-learned section added (AI citation
  audits can introduce plausible-but-wrong attributions; human expert review required
  before CGAL submission)
- papers/MANUAL-DOWNLOAD.md: overview of papers requiring manual download (paywalled
  journals, TU Berlin theses, books)
- .gitignore: papers/*.pdf excluded (downloaded arXiv PDFs, not tracked)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

doc/api/tests.md

@@ -7,7 +7,7 @@ Pure-math tests, only Eigen required. Covers Java utilities ported in Phase 1–
 | File | What it tests |
 |---|---|
 | `test_clausen.cpp` | Clausen Cl₂, Lobachevsky Л, ImLi₂ — values at known points |
-| `test_hyper_ideal_utility.cpp` | Tetrahedron volumes (Meyerhoff / Kolpakov–Mednykh) + Java golden-value oracle (Clausen/Л/ImLi₂, ζ₁₃/₁₄/₁₅/ζ, both volume formulas) |
+| `test_hyper_ideal_utility.cpp` | Tetrahedron volumes (Meyerhoff / Springborn 2008) + Java golden-value oracle (Clausen/Л/ImLi₂, ζ₁₃/₁₄/₁₅/ζ, both volume formulas) |
 | `test_matrix_utility.cpp` | Matrix helpers |
 | `test_surface_curve_utility.cpp` | Surface curve utilities |
 | `test_discrete_elliptic_utility.cpp` | Discrete elliptic functions |