docs: CLAUDE.md aktualisiert — Testzähler, Doku-Karte, geometry-central

- Testzähler korrigiert: 158 CGAL / 2 skips → 173 CGAL / 1 skip
- Neue Sektion "Key documentation for mathematical context": Tabelle der
  wichtigsten Nachschlagewerke für mathematische Aufgaben (discrete-conformal-
  theory.md, geometry-modes.md, geometry-central-comparison.md, etc.)
- Kompakter geometry-central Absatz: was es ist, was es nicht hat, warum
  Kreuz-Validierung sinnvoll ist — Scope-Information für neue Sessions
- Finder-Duplicates-Quirk entfernt (längst behoben)

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

CLAUDE.md

@@ -239,11 +239,30 @@ Two jobs in `.gitea/workflows/cpp-tests.yml`:
 
 Runner: `eulernest` — self-hosted Raspberry Pi, ARM64, Ubuntu 22.04. Docker image: `git.eulernest.eu/conformallab/ci-cpp:latest`. `test-cgal` needs `test-fast` to pass first (`needs: test-fast`).
 
-Expected results: **36 non-CGAL tests pass**, **158 CGAL tests pass, 2 skipped** (intentional `GTEST_SKIP` stubs for genus-2 homology and analytic HyperIdeal Hessian — these are Java features deferred to Phase 9).
+Expected results: **36 non-CGAL tests pass**, **173 CGAL tests pass, 1 skipped** (intentional `GTEST_SKIP` stub for analytic HyperIdeal Hessian — deferred to Phase 9b).
+
+## Key documentation for mathematical context
+
+When working on math-heavy tasks, read these before reasoning from scratch:
+
+| Question | Document |
+|---|---|
+| What is the mathematical problem this library solves? | `doc/math/discrete-conformal-theory.md` |
+| What are the three geometry modes and how do they differ? | `doc/math/geometry-modes.md` |
+| How does conformallab++ relate to geometry-central (CMU)? | `doc/architecture/geometry-central-comparison.md` |
+| What analytic results can be used to validate correctness? | `doc/math/validation.md` |
+| Which Java classes are ported, which are planned? | `doc/roadmap/java-parity.md` |
+| What does each processing function require/provide? | `doc/api/contracts.md` |
+
+**geometry-central** (Keenan Crane, CMU) implements the same discrete conformal
+equivalence problem (Gillespie, Springborn & Crane, SIGGRAPH 2021) but uses
+Ptolemaic flips on intrinsic triangulations instead of Newton on the original mesh.
+It has no period matrix, holonomy, or spherical geometry mode.
+The shared mathematical core (Springborn 2020) means cross-validation is meaningful.
+See `doc/architecture/geometry-central-comparison.md` for the full comparison.
 
 ## Known quirks
 
-- **Finder duplicate files**: `include/` contains files like `clausen 2.hpp`, `hyper_ideal_utility 2.hpp` — macOS Finder duplicates. Always use the canonical name without ` 2`. These should be deleted.
 - **`test-fast` also runs stubs**: `conformallab_tests` (non-CGAL) contains `GTEST_SKIP`-based stubs for functionals that need CGAL. This is intentional — those tests document what was in the Java port scope but requires the CGAL mesh type.
 - **Boost is header-only**: CGAL 6.x uses only Boost headers (`Boost.Config`, `Boost.Graph`). No compiled Boost libraries are needed. `find_package(Boost REQUIRED)` only locates the include path.
 - **`main` branch is protected** on `origin` (Gitea). Push to `dev`, then merge via pull request. Codeberg `main` can be pushed to directly.