Gaze: say why gaze mode can't work yet, and open the calibration whenever it's missing

Turning gaze mode on without a calibration opened Calibrate only on the
off-to-on change, and only if it could open right then. With the headset
off, the eye tracker silent, or the panel not built, or with gaze mode
already on when the gaze service started, nothing opened and nothing said
why: the pointer just stayed a mouse.

- The gaze service now checks every second: gaze mode on, no calibration
  for the tracker in use, eyes seen -> the full calibration opens. One
  that closes unfinished opens again only after the headset comes off and
  on, gaze mode off and on, or Calibrate, so it doesn't loop. A start that
  fails retries every 10 s.
- Its status says why gaze mode can't work yet (checks.problem): not
  calibrated and opening, open, closed unfinished, or can't open and why.
- Input Settings shows that under the Gaze pointer switch, along with the
  gaze service not installed or not running and our tracker missing its
  frame grabber.
- ft-gazectl on notes a missing calibration.

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

gaze/ft-gazectl

@@ -36,8 +36,17 @@ def main():
         if r is None:
             sys.exit("the pointer helper isn't running")
         print(f"gaze mode {r.removeprefix('ok ')}" if r else "no answer (an older pointer helper without gaze mode?)")
-        if ask("ft_gazed", "status", 0.3) is None:
+        st = ask("ft_gazed", "status", 0.3)
+        if st is None:
             print("note: the gaze service (ft-gazed) isn't running, so the pointer has no gaze to follow")
+        elif r == "ok on":
+            try:
+                calibrated = (json.loads(st).get("checks") or {}).get("calibrated")
+            except ValueError:
+                calibrated = None
+            if calibrated is False:
+                print("note: no calibration for this eye tracker yet; it opens in the headset "
+                      "(if it can't, ft-gazectl status says why: checks.problem)")
     elif cmd in ("status", "forget", "reload"):
         r = ask("ft_gazed", cmd)
         if r is None: