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/Makefile

@@ -0,0 +1,49 @@
+# Hand tracking, built into build/ (hands/build.sh runs this in the dev container):
+#   make          ft-camd (camd/: runs on the host, so linked statically) and ft-hands (track/)
+#   make tools    ft-handreplay and ft-ringplay, for recordings
+# The first build fetches ncnn (NCNN_TAG) and builds it into build/ncnn, which takes a few
+# minutes. NCNN=DIR uses an ncnn install already built instead.
+NCNN_TAG  = 20260526
+NCNN     ?= build/ncnn/install
+CFLAGS   ?= -O2 -g -Wall -Wextra -Wno-unused-parameter
+CXXFLAGS ?= -O2 -g -Wall -Wextra -Wno-unused-parameter -Wno-psabi
+CXXFLAGS += -std=c++17 -fopenmp -I$(NCNN)/include/ncnn
+LDLIBS    = $(NCNN)/lib/libncnn.a -ljsoncpp -fopenmp -lpthread
+
+CAMD  = camd/camd.c camd/tp.c camd/xrcams.c
+TRACK = track/calib.cpp track/nets.cpp track/tracker.cpp track/io.cpp track/record.cpp track/pinch.cpp
+HDR   = $(wildcard track/*.h) camd/fhring.h include/fh_hands.h include/fh_gestures.h
+
+all: build/ft-camd build/ft-hands
+tools: build/ft-handreplay build/ft-ringplay
+
+build/ft-camd: $(CAMD) camd/tp.h camd/xrcams.h camd/fhring.h
+	@mkdir -p build
+	$(CC) $(CFLAGS) -static -o $@ $(CAMD) -lm
+
+build/ft-hands: track/main.cpp $(TRACK) $(HDR) $(NCNN)/lib/libncnn.a
+	@mkdir -p build
+	$(CXX) $(CXXFLAGS) -o $@ track/main.cpp $(TRACK) $(LDLIBS)
+
+build/ft-handreplay: track/replay.cpp $(TRACK) $(HDR) $(NCNN)/lib/libncnn.a
+	@mkdir -p build
+	$(CXX) $(CXXFLAGS) -o $@ track/replay.cpp $(TRACK) $(LDLIBS)
+
+build/ft-ringplay: track/ringplay.cpp track/record.h camd/fhring.h
+	@mkdir -p build
+	$(CXX) $(CXXFLAGS) -o $@ track/ringplay.cpp
+
+# ncnn as frame-hands built it (the models were converted and quantized for it), minus its tools
+build/ncnn/install/lib/libncnn.a:
+	rm -rf build/ncnn && mkdir -p build/ncnn
+	git clone -q --depth 1 --branch $(NCNN_TAG) -c advice.detachedHead=false https://github.com/Tencent/ncnn.git build/ncnn/src
+	cmake -S build/ncnn/src -B build/ncnn/build -G Ninja -Wno-dev -DCMAKE_BUILD_TYPE=Release \
+	  -DCMAKE_INSTALL_PREFIX=$(CURDIR)/build/ncnn/install -DCMAKE_INSTALL_LIBDIR=lib -DNCNN_VULKAN=OFF \
+	  -DNCNN_OPENMP=ON -DNCNN_INT8=ON -DNCNN_SIMPLEOCV=ON -DNCNN_BUILD_TOOLS=OFF -DNCNN_BUILD_EXAMPLES=OFF \
+	  -DNCNN_BUILD_BENCHMARK=OFF -DNCNN_BUILD_TESTS=OFF -DNCNN_PYTHON=OFF > build/ncnn/cmake.log
+	cmake --build build/ncnn/build --target install > build/ncnn/build.log
+
+clean:
+	rm -f build/ft-camd build/ft-hands build/ft-handreplay build/ft-ringplay
+
+.PHONY: all tools clean