Bring our own eye tracker into the gaze folder, run by the gaze service

frame-eyes, a separate project until now, becomes gaze/tracker:
- ft-eyegrab (was fe-bufprobe) copies the eye-camera frames, read-only, out of
  SteamVR's eyetracking process. It runs as the system service
  frametop-eyegrab.service, which gaze/tracker/install.sh installs to
  /etc/frametop with sudo. It keeps only CAP_SYS_PTRACE, CAP_DAC_READ_SEARCH, and
  CAP_CHOWN, and copies frames only while /dev/shm/frametop-eyes-want is fresh,
  holding none of the tracker's buffers otherwise.
- ft-eyes (was fe-trackd) runs under ft-gazed in the dev container, with
  build/venv's pinned numpy and OpenCV: while Eye tracker is Own tracker, or on
  the probe's lease ("eyes SECONDS"). No sudo password or fe-live script at
  run time any more.
- lab/ holds the research tools (ft-eyes-score, -e2e, -record, -replay,
  -session) and findings.md. Recordings live outside the repo, in
  ~/.local/share/frametop/eyes/captures; .gitignore catches stray frame dumps.

Its socket is now @ft_eyes, its output /dev/shm/frametop-eyes-gaze, and its state
~/.local/state/frametop/gaze/eyes. On practice1 -> practice2 the whole live path
(ft-eyes-e2e) gives 1.30 deg median and 3.18 for the worst tenth, as before the
move (1.30, 3.21).

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

session/frametop.conf.example

@@ -30,7 +30,7 @@ POINTER_GAZE_RETAKE=5      # gaze mode: how far (degrees) you look away from the
 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
 POINTER_GAZE_HOLD=0.5      # gaze mode: a press held this long (s) without moving becomes a real press (to drag); moved or released sooner, it clicks where you let go
 POINTER_GAZE_SHOW=1        # gaze mode: the dot shows this long (s) after the mouse moves it; also while a press is held, and a pulse per click
-GAZE_TRACKER=steam         # gaze service: steam = SteamVR's eye tracker | own = our own (frame-eyes' fe-trackd, calibrated in the gaze probe with Own tracker)
+GAZE_TRACKER=steam         # gaze service: steam = SteamVR's eye tracker | own = our own (gaze/tracker: its frame grabber needs gaze/tracker/install.sh; calibrated in the gaze probe with Own tracker)
 GAZE_EYE=auto              # gaze service: eye bias. auto = each eye weighted by how far off it was at your recent nudges | left | right = that eye counts twice
 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)