Add gaze mode to the pointer: it goes where you look

MAGIC pointing (Zhai et al. 1999), off by default: with POINTER_GAZE=1,
"gaze on", or a button mapped to the new gaze_toggle action, the cursor ray
is the corrected gaze from ft-gazed while the gaze has the pointer. Moving
the mouse takes the pointer from where the gaze left it; looking more than
POINTER_GAZE_RETAKE (5 deg) away with the mouse still gives it back. The
pointer is aimed at the gaze, never steered toward it, and only fresh gaze
moves it, so a stopped service or a blink leaves it where it is. A mouse
nudge of up to POINTER_GAZE_NUDGE_MAX (8 deg) before a click is sent to
ft-gazed as a lesson in the eye tracker's error.

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

session/frametop.conf.example

@@ -23,6 +23,9 @@ POINTER_LEASH_DEG=10       # head follow: how far (degrees) your head can turn b
 POINTER_LEASH_DELAY=0.2    # head follow: how long (s) your head has to stay past the leash, so a glance doesn't move the cursor
 POINTER_LEASH_RETURN=0.2   # head follow: once it comes along, how quickly (s) the cursor settles back to its place in your view
 POINTER_FOLLOW_REACH=70    # head follow: how far (degrees) from the middle of your view the mouse can move the cursor
+POINTER_GAZE=0             # 1 = the pointer goes where you look, the mouse does the last bit (needs the gaze service: gaze/run.sh install)
+POINTER_GAZE_RETAKE=5      # gaze mode: how far (degrees) you look away from the pointer before the gaze takes it back from the mouse
+POINTER_GAZE_NUDGE_MAX=8   # gaze mode: a mouse nudge up to this far (degrees) before a click is learned as the eye tracker's error
 META_DASHBOARD=0   # 1 = a Meta tap on a pass-through keyboard toggles the SteamVR dashboard (pointer mode only)
 SHARE_KEYS=0       # 1 = keys of keyboards grabbed for the desktop also go to @frametop_keys, for hotkey tools (any local process can listen)
 LAYOUT_GRAB_OFFSET=0.075   # arranging screens: where the floating window's grab bar is, in metres below the screen