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>

doc/architecture/project-structure.md

@@ -14,7 +14,7 @@ ConformalLabpp/
 │   │   ├── constants.hpp             # conformallab::PI, TWO_PI
 │   │   ├── clausen.hpp               # Cl₂, Lobachevsky Л, ImLi₂
 │   │   ├── hyper_ideal_geometry.hpp  # ζ₁₃/₁₄/₁₅, lᵢⱼ, αᵢⱼ, σᵢ, σᵢⱼ
-│   │   ├── hyper_ideal_utility.hpp   # Tetrahedron volumes (Meyerhoff / Springborn 2008)
+│   │   ├── hyper_ideal_utility.hpp   # Tetrahedron volumes (Ushijima 2006 / Springborn 2008)
 │   │   ├── hyper_ideal_visualization_utility.hpp  # Poincaré disk projection, circumcircle helpers
 │   │   ├── hyper_ideal_functional.hpp # HyperIdeal energy + gradient on ConformalMesh
 │   │   ├── hyper_ideal_hessian.hpp   # HyperIdeal Hessian (symmetric FD, Phase 9b: analytic)