fix+test: Euclidean holonomy/τ end-to-end + spherical edge-DOF oracle (2026-05-29 audit)

Bundles the 2026-05-29 Java↔C++ math-correctness audit (doc/reviewer/
java-port-audit.md, 11 findings) with two follow-up fixes.

Audit code changes:
- Finding 3 (spherical_functional): edge-DOF replacement parameterization via
  spher_eff_lambda; edge gradient α_opp⁺+α_opp⁻−θ_e (drops additive −(S⁺+S⁻)/2)
- Finding 4 (spherical_hessian): always-compiled edge-DOF throw guard
- Finding 6 (period_matrix): faithful normalizeModulus (0≤Re≤½, Im≥0, |τ|≥1)
- Finding 9 (inversive_distance): degenerate-face limiting angles, no skip
- Findings 1/2 (euclidean): degenerate gradient limiting angles + Hessian guard

Euclidean holonomy/τ fix: develop the cut surface across the dual spanning tree
only (cut_graph now exposes is_dual_tree), so genus-1 cut edges yield
non-degenerate lattice generators. Previously τ came out 0 / NaN / 1e13 on the
bundled tori; now matches the analytic revolution modulus i·√(R²−r²)/r. Re-enabled
τ reporting in the Euclidean CLI; rewrote validation.md §3/§4 accordingly.

Tests (240 CGAL, 0 skipped):
- HolonomyEndToEnd ×3 — tori of revolution (4×4, hex 6×6, 8×8) vs analytic modulus
- SphericalFunctional.EdgeGradient_RegularTetClosedForm — independent closed-form
  π/3 oracle locking the Finding-3 edge formula (the path-integral FD check cannot
  detect a wrong-but-conservative gradient)

Also documents the latent spherical/hyperbolic holonomy-extraction bug (same
single-development pattern, dead code today) in research-track.md (Phase 9c/10),
and adds favour/normalisations to the codespell ignore list.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

doc/roadmap/research-track.md

@@ -293,6 +293,20 @@ The phase numbers match `doc/roadmap/phases.md`.
   the cut-graph + holonomy infrastructure already in conformallab++).
 * **Effort:** large (10–14 days).
 * **Status:** roadmap item, no PR yet.
+* **Known prerequisite bug (latent, 2026-05-29):** the holonomy-extraction
+  blocks in `spherical_layout` and `hyper_ideal_layout` (`layout.hpp`)
+  repeat the flawed single-development pattern that produced garbage τ for
+  the Euclidean path before the 2026-05-29 fix.  They read the
+  translation / Möbius deck transformation from one full-surface
+  development plus a one-sided apex trilateration, instead of developing
+  across only the **dual** spanning tree and measuring the shared-edge
+  displacement between two independent developments (as the corrected
+  `detail::euclidean_holonomy` now does).  These blocks are currently dead
+  code — every caller passes `holonomy == nullptr` — but Phase 9c/10b will
+  exercise the hyperbolic path.  Fix = add `detail::spherical_holonomy` /
+  `detail::hyperbolic_holonomy` mirroring `detail::euclidean_holonomy`.
+  The hyperbolic mirror additionally needs `cpp_dec_float_50` (group-relation
+  product ∏gᵢ = Id overflows `double`; see CLAUDE.md high-precision note).
 
 ---