Make hand tracking a Frametop component

- Programs: ft-camd (the camera broker), ft-hands (the tracker), and
  ft-handreplay and ft-ringplay for recordings, built by hands/build.sh
  into hands/build/ with one Makefile. The first build fetches ncnn at
  frame-hands' pinned tag and builds it with the same options.
- ft-camd gets its privileges from file capabilities (CAP_SYS_PTRACE,
  CAP_PERFMON, CAP_DAC_READ_SEARCH) that hands/run.sh install sets with
  sudo, and drops them once set up. It still works under sudo. It runs
  on the host, linked statically, as frametop-camd.service. ft-hands
  runs in the dev container as frametop-hands.service. Both start and
  stop with SteamVR.
- Files move to /run/user/UID/frametop/ (cam-ring, hands, gestures),
  not $XDG_RUNTIME_DIR, which a terminal in the Frametop desktop has
  its own of. SIGUSR1 recordings go to ~/.local/share/frametop/hands.
- The calibration is read through /run/host in the container.
- Settings: HANDS_SWAP_SIDES and HANDS_CPUS in frametop.conf.
- install.sh offers hand tracking as an optional last step.
- The container gets jsoncpp-devel, glibc-static, and NumPy and OpenCV
  for the Python tools.
- tools/ring.py reads the ring, and models/NOTICE credits the
  Apache-2.0 models.

Checked: ft-handreplay gives identical summaries and byte-identical
depth dumps to frame-hands' fh-replay on both 2026-09-29 recordings.

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

hands/models/NOTICE

@@ -0,0 +1,12 @@
+The models in ncnn/ are converted from the OpenCV Zoo ONNX ports of Google's MediaPipe hand
+models, by tools/convert_models.py:
+
+- palm.ncnn.*: palm_detection_mediapipe_2023feb (https://huggingface.co/opencv/palm_detection_mediapipe)
+- hand.ncnn.*: handpose_estimation_mediapipe_2023feb (https://huggingface.co/opencv/handpose_estimation_mediapipe)
+
+MediaPipe is Copyright Google LLC. The models and the OpenCV Zoo ports are licensed under the
+Apache License, Version 2.0 (https://www.apache.org/licenses/LICENSE-2.0).
+
+Changes made here: converted to ncnn with pnnx, with the palm detector's channel pads
+rewritten as ncnn Padding layers, and quantized to 8 bits (the *-int8.ncnn.* files) with
+ncnn's tools.