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>

.gitignore

@@ -5,3 +5,9 @@ target/
 captures/
 __pycache__/
 frametop-report-*.txt
+# Eye-camera recordings (biometric) never go in the repo: they live in
+# ~/.local/share/frametop/eyes/captures. These catch strays (frame dumps, a lab venv).
+*.raw
+*.pgm
+.venv/
+.frame-job.d/