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/frametop-hands.service

@@ -0,0 +1,20 @@
+# Template: the installer replaces @REPO@ with the repo path on the Frame.
+[Unit]
+Description=Frametop hand tracking: hands for the screens' hand cutouts, pinches for the pointer
+Documentation=file://@REPO@/hands/README.md
+After=steamvr.service frametop-camd.service
+Wants=frametop-camd.service
+PartOf=steamvr.service
+
+[Service]
+# In the dev container (it's built against Fedora's libraries). It reads ft-camd's ring and
+# writes /run/user/UID/frametop/hands and gestures. Settings: HANDS_* in ~/.config/frametop.conf.
+ExecStartPre=-@REPO@/scripts/container-up.sh
+ExecStartPre=-/usr/bin/pkill -x ft-hands
+ExecStart=%h/.local/bin/distrobox enter dev -- @REPO@/hands/build/ft-hands --status 60
+Restart=always
+RestartSec=5
+TimeoutStopSec=5
+
+[Install]
+WantedBy=steamvr.service