docs(pose_3d): tags multi-camera + calibrazione cross-camera

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

CLAUDE.md

@@ -23,7 +23,7 @@ Useful endpoints (all under `http://localhost:8890`):
 - Grasp: `POST /api/grasp/plan`, `POST /api/grasp/execute` (set `dry_run` to gate G1 mutations).
 - Wrist/EE: `GET /api/wrist`, `POST /api/wrist/{absolute,relative,hand,emergency_stop,unlock}`.
 - Right arm: `GET /api/right_arm/state`, `POST /api/right_arm/detect_{front,wrist}`, `POST /api/right_arm/move_toward`, `POST /api/right_arm/{home,custom_pose}`.
-- Pose 3D: `GET /api/pose_3d/state` (wrist + joints + config), `POST /api/pose_3d/apply`, `GET /api/pose_3d/clouds` (Nuwa + D435i point clouds), `CRUD /api/pose_3d/poses/{name}`.
+- Pose 3D: `GET /api/pose_3d/state` (wrist + joints + config, incl. `cross_camera` calibration), `POST /api/pose_3d/apply`, `GET /api/pose_3d/clouds` (Nuwa + D435i point clouds), `GET /api/pose_3d/tags` (ArUco su Nuwa polso + D435i frontale), `POST /api/pose_3d/align?align_id=N` (fit Umeyama Nuwa→frontale, persiste in `pose_3d.cross_camera`), `CRUD /api/pose_3d/poses/{name}`.
 
 Tests live under `tests/` and run with `uv run pytest`. No linter is configured.
 
@@ -94,6 +94,7 @@ Marker-finder caveat: it uses **D435i intrinsics baked into its config** that do
 - **Pose 3D graceful offline:** `GET /api/pose_3d/state` returns 200 even when G1 is unreachable — `wrist` and `joints` are `null`, `robot_error` carries the message. The tab must remain usable for editing config / named poses / viewing the URDF model without a live robot.
 - **Pose 3D clouds:** `GET /api/pose_3d/clouds` acquires from Nuwa (eye-in-hand, polso DX) and D435i (front camera, torso) in parallel. Both are returned in **OpenCV optical frame** (X right, Y down, Z forward). The client attaches them to URDF links with configurable offset/rpy from `config.yaml > pose_3d.clouds`.
 - **Pose 3D joints mirroring:** `G1Client.diagnostics()` → `motors[].{name, q}` gives real joint positions in radians. The frontend uses these to pose the URDF model directly, bypassing client-side IK.
+- **Pose 3D cross-camera alignment:** `POST /api/pose_3d/align` fits an Umeyama similarity (rotation + translation + uniform scale) mapping Nuwa-optical → D435-optical from a tag (`align_id`) seen by both cameras, and persists it to `config.yaml > pose_3d.cross_camera`. The frontend renders the Nuwa cloud through the D435i transform pipeline (`d435LocalMatrix()` · alignMatrix) when `cross_camera.enabled`. If the tag isn't seen by both cameras, the saved matrix is NOT overwritten and the Nuwa cloud falls back to URDF placement. Tag detection (`GET /tags`) runs on both cameras; the GUI draws Nuwa tags red, D435i tags cyan.
 - Endpoints return `{ ..., "timings_ms": {step: ms, ..., total: ms} }`. New endpoints should follow this with `Stopwatch().step(name)`.
 - Calibration paths in config (`calibration.file`, `calibration.samples_file`) are resolved against `PRESA_MANO_DATA` when relative — see `_deps.calibration_file_path()` / `samples_file_path()`.
 - Italian is fine in user-facing copy (GUI, README, comments) — it's the project default.