Hands: park hand tracking behind ft-handsctl

Hand tracking no longer starts with SteamVR: hands/run.sh install leaves
the units disabled and links hands/ft-handsctl into ~/.local/bin, which
turns it on and off (on | off | status | log | cutouts on|off | gestures).
With it on, hands show through the screens; pinches and grips move the
pointer only with POINTER_HANDS=1, now off by default. ft-camd's service
runs the mono cameras only: while the headset is worn, the colour module
writes just a half-size image into the top-left quarter of its buffers,
which ft-camd can't use yet.

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

hands/frametop-camd.service

@@ -10,9 +10,10 @@ PartOf=steamvr.service
 # On the host: the dev container can't reach XRService. Its file capabilities (set by
 # hands/run.sh install) let it borrow the buffers; it drops them once set up. It exits when
 # XRService restarts, and comes back to attach to the new one.
-# The colour cameras run at 2 fps (their brightness picks the tracking cameras) until
-# ft-hands asks for more; HANDS_CAMERAS=mono leaves them out.
-ExecStart=@REPO@/hands/build/ft-camd --with-color --status 60
+# Mono cameras only: while the headset is worn the colour module writes only a half-size
+# image into the top-left quarter of its buffers (2026-09-30), which ft-camd can't use yet.
+# Add --with-color to try the colour cameras (ft-hands then picks them by the light).
+ExecStart=@REPO@/hands/build/ft-camd --status 60
 Restart=always
 RestartSec=5
 TimeoutStopSec=5