Defer hand tracking; the README leads with what Frametop does now

- install.sh no longer offers hand tracking (it's heavy on the CPU and
  needs more work); hands/ still builds and installs by hand
- the build container drops python3-opencv and python3-numpy, which
  only hand tracking's tools used: Fedora's OpenCV pulls in over a GB
- README: a new opening and feature list, the Use section by topic
  (screens, mouse, floating windows, profiles, gaze), and new known
  limitations

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

setup/dev-container.sh

@@ -18,9 +18,11 @@ packages=(
   mesa-libgbm-devel wayland-devel vulkan-loader-devel vulkan-headers plasma-wayland-protocols wlroots-devel
   # ft_pointer SteamVR driver: static C++ runtime (the host has an older glibc)
   libstdc++-static
-  # hand tracking: ft-hands reads the calibration with jsoncpp; ft-camd runs on the host, linked
-  # statically; the Python tools (hands/tools) need NumPy and OpenCV
-  jsoncpp-devel glibc-static python3-numpy python3-opencv
+  # hand tracking (deferred: not installed by install.sh; hands/run.sh install builds it): ft-hands
+  # reads the calibration with jsoncpp; ft-camd runs on the host, linked statically. Its Python
+  # tools (hands/tools) need NumPy and OpenCV, which aren't here: Fedora's python3-opencv pulls
+  # in over a gigabyte (hands/README.md says how to get them)
+  jsoncpp-devel glibc-static
   # Frametop Input Settings app (Kirigami, PySide6)
   python3-pyside6 kf6-kirigami kf6-qqc2-desktop-style qt6-qtwayland breeze-icon-theme plasma-breeze
   # Frametop remote desktop (VNC bridge through krdp)