Faithful port of the Unity CRAB UFOV mini-game. 4 subtasks
(CENTRAL_SOLO -> PERIPHERAL_SOLO -> CENTRAL_AND_PERIPHERAL ->
CENTRAL_AND_PERIPHERAL_AND_DISTRACTORS); tutorial walks all 4, test
phase only runs the 4th.

Trial flow: BLANK -> CUE -> MASK -> answer(s). Practice blank=30
frames, mask=40, presentation [16,30,44,60,68,76,84,92]. Test
blank=random[12,60], mask=19, presentation 3-down/1-up staircased
(start 12, min 1, max 99; step 2 pre-3rd-reversal, 1 post). Stops at
72 trials, 8 reversals, or 10 streaks at floor/ceiling.

Hand-rolled requestAnimationFrame + performance.now() timing via
rafSleep(ms). Eccentricities 2/4 deg practice 2-ring, 3/5/7 deg test
3-ring. 8-direction radar stage + central 2-AFC short/long panel.

4 locales (FR/IT/DE/EN), all with full UI strings + full audio
(147 OGGs) and 9 sprites copied verbatim from Unity. UFOV is fully
adaptive in Unity (no per-form sequences) so no Form selection.