feat: output_uv_map for InversiveDistance, error for CP-Euclidean, reviewer trio

Three reviewer-meeting deliverables in one commit.

(1) output_uv_map for the two remaining DCE entries
    ─────────────────────────────────────────────────
    * Discrete_inversive_distance.h: full implementation.  After Newton,
      reconstruct effective Euclidean edge lengths from the converged
      log-radii via the Bowers-Stephenson identity
      `ℓᵢⱼ² = rᵢ² + rⱼ² + 2·Iᵢⱼ·rᵢ·rⱼ`, populate a temporary
      EuclideanMaps with `lambda0 = log(ℓᵢⱼ²)`, and reuse the existing
      `euclidean_layout(mesh, 0, eucl)` priority-BFS.  Per-vertex
      Point_2 coordinates written into the user-supplied pmap.
      Optional `normalise_layout(true)` applies the canonical PCA
      centroid + major-axis rotation, same as the other 3 entries.

    * Discrete_circle_packing.h: throws std::runtime_error with a
      clear pointer to Phase 9c rather than silently producing
      nonsense.  CP-Euclidean is face-based; the faithful output is a
      per-face circle packing in ℝ², not a per-vertex Point_2 map.
      A true layout requires BPS-2010 §6 (~150 lines, on the porting
      roadmap as Phase 9c).  Failing loudly is the honest default.

    Tests: 2 new cases in test_cgal_phase8b_lite.cpp
    (OutputUvMap_InversiveDistance_PopulatesPmap;
    OutputUvMap_CPEuclidean_ThrowsClearly).  Both green.
    Suite total now 259 (was 257, +2).  CGAL subtotal: 234 → 236.

(2) Reviewer meeting documents
    ──────────────────────────
    New directory doc/reviewer/ with three files:

    * briefing.md  — one-page orientation for the reviewer.
      What the project is, where to look first
      (https://tmoussa.codeberg.page/ConformalLabpp/), the headline
      evidence (tests/coverage/sanitizers/license), what we want from
      them, what's deferred and why, and the 5 questions in a separate
      file.

    * questions.md — the 5 concrete decisions we want their second
      opinion on:
        Q1 Phase 9c (port-literal vs re-derive)
        Q2 Phase 9b-analytic (worth ~2 weeks for ~6× speedup?)
        Q3 CP-Euclidean output_uv_map (build now or defer?)
        Q4 CGAL submission strategy (one package or five?)
        Q5 geometry-central cross-validation co-authorship
      Plus an explicit "what would you say no to?" question at the
      bottom — negative feedback is the highest-value information.

    * agenda.md   — my own internal playbook (NOT to be sent).
      60-min flow: 5-min thank-you, 10-min architecture tour,
      30-min for Q1-Q5 in the order Q4-Q1-Q2-Q5-Q3, 5-min "no"
      question, 5-min wrap-up.  Includes post-meeting memo template
      to fill out in the 30 min after.

    * README.md    — index for the directory; says which file goes
      to whom and when to send.

(3) locked-vs-flexible.md known-limitations update
    ─────────────────────────────────────────────
    "output_uv_map covers 3 of 5 entries" → "covers 4 of 5".
    CP-Euclidean's throws-clearly behaviour documented as a Phase 9c
    deliverable rather than a passive gap.

Bonus: extended .codespellrc ignore list (acknowledgement, the
British-English spelling I used in agenda.md).

Verifications on this commit:
  259/259 tests pass (0 skipped)
  scripts/check-test-counts.sh:                OK (23 + 236 = 259)
  scripts/quality/license-headers.sh:          OK (66/66 SPDX)
  python3 scripts/quality/cgal-conventions.py: OK (0/6 violations)
  scripts/quality/codespell.sh:                OK (0 typos)
  scripts/quality/shellcheck.sh:               OK (0 findings)
  python3 scripts/check-markdown-links.py:     OK (143/143)

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

doc/reviewer/README.md

@@ -0,0 +1,28 @@
+# Reviewer meeting materials
+
+A single landing page for the three documents associated with the
+external-reviewer meeting (Springborn/Bobenko alumnus, May 2026).
+
+| Document | Audience | Purpose |
+|---|---|---|
+| [`briefing.md`](briefing.md) | **the reviewer** | one-page orientation: what the project is, where to look first, what we want from them |
+| [`questions.md`](questions.md) | **the reviewer** | the 5 concrete decisions we want their opinion on (skim before the meeting) |
+| [`agenda.md`](agenda.md) | **me** | my own meeting playbook: timing, order, the "no" question, post-meeting memo template |
+
+After the meeting, a fourth file `2026-XX-XX-meeting-notes.md` should
+land here too — the memo template at the bottom of `agenda.md` is the
+suggested structure.
+
+## When to send to the reviewer
+
+- **briefing.md** + **questions.md**: as part of the meeting-confirmation
+  email, ~5 business days before the meeting.  Subject line: *"Pre-read
+  for our conformallab++ chat (~15 min)"*.
+- **agenda.md**: never send.  This is internal scaffolding.
+
+## Quick links the reviewer should bookmark
+
+- 🌐 Reviewer-hub landing page: <https://tmoussa.codeberg.page/ConformalLabpp/>
+- 📦 Source: <https://codeberg.org/TMoussa/ConformalLabpp>
+- 📝 Architecture decisions: [`../architecture/locked-vs-flexible.md`](../architecture/locked-vs-flexible.md)
+- 📐 Schläfli derivation (for Q2): [`../math/hyperideal-hessian-derivation.md`](../math/hyperideal-hessian-derivation.md)