fix(citations): correct Meyerhoff/Ushijima misattribution

DOI 10.1007/0-387-29555-0_13 is Ushijima (sole author) —
"A Volume Formula for Generalised Hyperbolic Tetrahedra",
in: Prékopa & Molnár (eds.), Non-Euclidean Geometries,
Springer 2006. arXiv: math/0309216.

The references.md entry was wrong on all three counts:
  - Author:  "Meyerhoff, Ushijima" → Ushijima only
  - Title:   "A Note on the Dirichlet Domain" → entirely different title
  - Book:    "The Epstein Birthday Schrift" → Non-Euclidean Geometries

Same error pattern as the Kolpakov-Mednykh fix: the Java source
links only to a DOI without naming authors; a wrong name was
invented during the C++ port.

Files corrected: hyper_ideal_utility.hpp, hyper_ideal_functional.hpp,
references.md, tests.md, project-structure.md, finding-orchestration.md,
math-derivation-citation-audit.md, MANUAL-DOWNLOAD.md

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

code/include/hyper_ideal_functional.hpp

@@ -374,7 +374,7 @@ static FaceAngles compute_face_angles(
 /// Per-face energy contribution U(f) before subtracting the θ·a and Θ·b terms.
 ///
 /// Supported configurations (faithful port of HyperIdealFunctional.java):
-///   * All three vertices hyper-ideal (v?b = true)       → Meyerhoff/Ushijima volume
+///   * All three vertices hyper-ideal (v?b = true)       → Ushijima 2006 volume
 ///   * Exactly one vertex ideal (v?b = false, other two true) → Springborn 2008 volume
 ///
 /// NOT supported — faces with two or three ideal vertices.  The Java reference

code/include/hyper_ideal_utility.hpp

@@ -16,7 +16,8 @@
 namespace conformallab {
 
 /// Volume of a generalized hyperbolic tetrahedron with dihedral
-/// angles `A,…,F` via the Meyerhoff / Ushijima 2006 formula.
+/// angles `A,…,F` via the Ushijima 2006 formula (DOI 10.1007/0-387-29555-0_13,
+/// arxiv math/0309216). Note: sole author is Ushijima; "Meyerhoff" is not an author.
 /// Same as Java `HyperIdealUtility.calculateTetrahedronVolume()`.
 inline double calculateTetrahedronVolume(double A, double B, double C,
                                          double D, double E, double F) {