Hands: ft-hands works out which side camera is which

ft-camd tells the side cameras apart by XRService's buffer allocation order,
which some XRService starts reverse; both of 2026-10-02's starts did, so the
cutouts missed the hands. HANDS_SWAP_SIDES=auto (the default) has ft-hands
vote from hands seen in both side cameras: the landmark rays meet in front
of both cameras only under the right naming. While undecided it probes the
exchanged naming with the landmark model. It decides in about 2 s of hands
(right on all 7 recordings replayed), swaps the views in place, and publishes
sides.json. 0 and 1 still force it, with a warning when the hands disagree.

Recordings carry each part's naming and the session's decision; review,
export, validate and ft-handreplay put the names right, and takes.py sides
records a decision by hand.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

hands/rec/tests/test_validate.py

@@ -68,7 +68,8 @@ def make_session(base, contributor=None, sid=None, device=True):
                       "rings": False, "watch": False, "notes": ""},
         "device": {"steamos": "3.8", "steamvr": "r25358740+28b72a4f-1", "cameras": [{"name": n, "width": w, "height": h}
                                                                  for n, w, h in CAMS]},
-        "calibration_removed": ["serial"], "takes": ["01-hand-size", "02-no-hands"], "status": "done"})
+        "calibration_removed": ["serial"], "takes": ["01-hand-size", "02-no-hands"], "status": "done",
+        "sides": {"swapped": False, "decided_by": "auto", "state": "confirmed"}})
     takes.write_json(os.path.join(sdir, "calibration.json"),
                      {"cameras": [{"name": "slam_left", "intrinsics": [1.0, 2.0, 3.0]}]})
     if device: