feat(data-only-viz): SMPLer-X fork + submodule

Fork electron-rare/SMPLer-X (S-Lab License 1.0, non-comm
seulement) ajoute en git submodule a third_party/SMPLer-X.
Setup script utilise le submodule au lieu de cloner upstream.
pyproject : nouvel extra 'smplerx' (torch + mmcv-lite +
ultralytics + smplx + timm). NOTICE.md documente la posture
non-commerciale heritee de Multi-HMR et SMPLer-X.

Le portage inference ARM Mac est l'etape suivante : SMPLer-X
vendorise sa propre mmpose (transformer_utils/mmpose), donc
seul mmcv.Config a besoin d'un substitut (mmcv-lite). Le
detecteur mmdet sera remplace par YOLO Ultralytics.

NOT YET DONE: smpler_x_worker.py (model load + inference,
~1 j) ; bench camera ; integration main.py.

NOTICE.md

@@ -0,0 +1,40 @@
+# AV-Live Third-Party Notices
+
+AV-Live includes or depends on the following third-party works,
+which are licensed under their own terms.
+
+## Body Mesh Recovery Models
+
+### Multi-HMR (NAVER, 2025)
+
+- **License**: NAVER Non-Commercial License
+  (https://github.com/naver/multi-hmr/blob/main/LICENSE.txt)
+- **Use**: Non-commercial only. Body mesh recovery from camera input.
+- **Integration**: model checkpoint downloaded at runtime to
+  `~/.cache/av-live-multihmr/`. No source code vendored.
+
+### SMPLer-X (S-Lab, ECCV 2024)
+
+- **License**: S-Lab License 1.0
+  (`third_party/SMPLer-X/LICENSE` after submodule init)
+- **Use**: Non-commercial only. Whole-body mesh recovery (SMPL-X).
+- **Integration**: vendored as git submodule at
+  `third_party/SMPLer-X` (fork `electron-rare/SMPLer-X`, kept in
+  sync with `caizhongang/SMPLer-X` or its current upstream).
+- **Modifications in fork**: minimal patches for ARM macOS Python
+  3.14 inference (replace mmdet detector with Ultralytics YOLO,
+  shim `mmcv.Config` via `mmcv-lite`).
+
+## Implication
+
+**AV-Live integrates non-commercial-only model code from Multi-HMR
+and SMPLer-X.** Commercial deployment (paid performances, packaged
+installations sold to clients) requires either :
+
+1. Obtaining commercial licenses from NAVER and S-Lab respectively, OR
+2. Replacing both integrations with MIT/Apache-licensed alternatives
+   (see `docs/superpowers/plans/2026-05-13-modern-body-mesh-survey.md`
+   for candidates like Fast-SAM-3D-Body which is MIT-licensed).
+
+The AV-Live source code itself (sound_algo, oscope-of, launcher,
+data_only_viz integration glue) is under GPL-3.0 (see root LICENSE).