docs: restructure documentation into focused files

README.md: reduced from 703 to ~75 lines — what/why, status, quick
start, minimal usage example, navigation table to doc/ files.

doc/architecture/overall_pipeline.md: trimmed — roadmap, extension
points, declarative pipeline YAML, and references sections removed
(each now has its own dedicated file). Replaced with a link table.

New files:
  doc/getting-started.md       — build modes, single-test invocation, CLI
  doc/api/pipeline.md          — full pipeline API with code for all 3 geometries
  doc/api/extending.md         — new functionals, geometry modes, Java porting guide
  doc/api/contracts.md         — processing unit preconditions/provides table
  doc/api/cgal-package.md      — Phase 8 CGAL package design + YAML pipeline (TODO)
  doc/math/geometry-modes.md   — Euclidean/Spherical/HyperIdeal comparison
  doc/math/references.md       — all papers by module
  doc/roadmap/phases.md        — Phases 1–10 with porting/research boundary
  doc/roadmap/java-parity.md   — Java vs C++ feature parity table
  doc/contributing.md          — language policy, test standards, release flow

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

doc/math/references.md

@@ -0,0 +1,35 @@
+# References
+
+## Primary source
+
+This library implements the algorithms from:
+
+| | |
+|---|---|
+| **Sechelmann** — *Variational Methods for Discrete Surface Parameterization: Applications and Implementation*, Doctoral thesis, TU Berlin 2016 | The complete mathematical foundation: discrete conformal equivalence, variational angle-sum functionals, Newton solver, uniformization, period matrices, holonomy. DOI: [10.14279/depositonce-5415](https://depositonce.tu-berlin.de/items/8e2988b2-d991-45b5-aad5-9fb7988f3b2f) · CC BY-SA 4.0 |
+
+Java reference implementation: [github.com/varylab/conformallab](https://github.com/varylab/conformallab)
+
+---
+
+## References by module
+
+| Reference | Used in |
+|---|---|
+| **Springborn** — *Ideal Hyperbolic Polyhedra and Discrete Uniformization*, Discrete & Computational Geometry (2020) | `hyper_ideal_geometry.hpp` — ζ₁₃/ζ₁₄/ζ₁₅ functions; `hyper_ideal_functional.hpp` |
+| **Pinkall, Polthier** — *Computing Discrete Minimal Surfaces and Their Conjugates*, Experimental Mathematics (1993) | `euclidean_hessian.hpp` — cotangent Laplacian |
+| **Bobenko, Springborn** — *Variational Principles for Circle Patterns and Koebe's Theorem*, Transactions AMS (2004) | Variational angle-sum framework underlying all three functionals |
+| **Luo** — *Combinatorial Yamabe Flow on Surfaces*, Communications in Contemporary Mathematics (2004) | Inversive-distance functional — **not yet ported**, Phase 9a |
+| **Erickson, Whittlesey** — *Greedy Optimal Homotopy and Homology Generators*, SODA (2005) | `cut_graph.hpp` — tree-cotree algorithm |
+| **Bobenko, Springborn** — *A Discrete Laplace–Beltrami Operator for Simplicial Surfaces*, Discrete & Computational Geometry (2007) | Background for cotangent weights |
+| **Desbrun, Kanso, Tong** — *Discrete Differential Forms for Computational Modeling*, SIGGRAPH Course Notes (2006) | Discrete exterior calculus background for Phase 10a |
+
+---
+
+## Phase 10 references (future research)
+
+| Reference | Relevant for |
+|---|---|
+| **Farkas, Kra** — *Riemann Surfaces*, Springer GTM 71 | Siegel period matrix, Teichmüller theory |
+| **Siegel** — *Topics in Complex Function Theory, Vol. 2*, Wiley | Siegel upper half-space H_g, Sp(2g,ℤ) reduction |
+| **Bobenko, Mercat, Schmies** — *Period Matrices of Polyhedral Surfaces*, in: Computational Approach to Riemann Surfaces (2011) | Discrete period matrices on polyhedral surfaces |