docs: Layout2D index semantics, CLI table, CLI roadmap (U9+U10+U11)

U9 (layout.hpp + example_layout.cpp)
  Layout2D.uv and .halfedge_uv now have explicit Doxygen docs stating:
    - indexing: v.idx() / h.idx() (raw integer index)
    - length: mesh.number_of_vertices() / number_of_halfedges()
    - precondition: no vertex removal / collect_garbage() after loading
    - access pattern example in the doc comment
  example_layout.cpp: access site comment + static_cast<size_t>(v.idx())

U10 (getting-started.md)
  New 'CLI parameter reference' table (7 rows) added directly below the
  CLI usage examples; cross-references --help as the canonical source

U11 (doc/roadmap/phases.md)
  New Phase 9h 'CLI usability extensions' section inserted before Phase 10:
    9h.1  --tol / --max-iter solver-tuning params  (~30 min, no deps)
    9h.2  -g cp_euclidean / -g inversive_distance  (~2-4 h, needs 9a ✅)
  Each sub-task has effort estimate, implementation sketch, and
  acceptance criteria so a future session can pick it up cold.

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

doc/roadmap/phases.md

@@ -287,6 +287,37 @@ mesh type.
            no new library surface).  Effort: small (~2–3 days).
 ```
 
+9h — CLI usability extensions  (infrastructure — no Java equivalent)
+──────────────────────────────────────────────────────────────────
+
+Identified by usability-audit-2026-05-31 (Finding-U11).  Two independent
+sub-tasks; either can land independently.
+
+```
+9h.1   Newton solver tuning parameters  (~30 min)
+         Currently hardcoded in all three run_*() helpers:
+           tol = 1e-8, max_iter = 200
+         Add to conformallab_cli.cpp:
+           app.add_option("--tol",      tol,      "Newton gradient tolerance [1e-8]");
+           app.add_option("--max-iter", max_iter, "Newton iteration limit    [200]");
+         Thread both through run_euclidean / run_spherical / run_hyper_ideal.
+         Update getting-started.md CLI parameter table.
+         Status: 🔲 planned.  Effort: ~30 min.  No dependencies.
+
+9h.2   Phase-9a models in CLI  (~2–4 hours)
+         The CP-Euclidean and Inversive-Distance functionals are fully
+         implemented in the library and exposed via the CGAL public API
+         (Discrete_circle_packing.h, Discrete_inversive_distance.h), but
+         a CLI user cannot reach them.  Add:
+           -g cp_euclidean       → run_cp_euclidean()
+           -g inversive_distance → run_inversive_distance()
+         Following the existing run_euclidean() pattern (~60 lines each).
+         Add both geometry strings to the CLI::IsMember validator.
+         Update README + getting-started.md parameter table.
+         Status: 🔲 planned.  Effort: ~2–4 h.  Requires: 9a complete ✅.
+         Java reference: none (both functionals are research / literature ports).
+```
+
 ---
 
 ## ◼ New research directions — Phases 10d–10g  (2026 library scan)