Implements the recurrent 4D (px, py, vx, vy) accumulation buffer per the
2026-06-09 design (cuas_rt_gpu-internal CONTINUE.md, Step 4):

- Update rule: buf = leak*(1-w_eff)*shift(buf, v) + w_eff*conditioned(meas),
  applied every curt_recur_period (default 4) time units so the per-update
  pixel shift is integer-clean (1 px per minimum velocity step).
- shift(): each 4D point moves by its own velocity; predictions leaving the
  ROI are dropped.
- conditioned(): adaptive 4D spreading of filterConv5dROI survivors -
  dimensions spanned by adjacent survivors are "resolved" and not expanded;
  total spread weight per survivor is 1.
- w_eff: fixed curt_recur_w, or per-pixel adaptive w*tanh(strength/wthresh)
  when curt_recur_wthresh > 0 (dark frames then decay by curt_recur_leak
  alone - blind prediction).
- convolve3d() still runs at every time step with unchanged output files;
  the buffer consumes every curt_recur_period-th ROI output (level 0 only).
- New params (curt_recur_en/period/w/leak/wthresh/spread) plumbed through
  IntersceneMatchParameters (dialog, get/set, properties, copy).
- Buffer state snapshots saved as -RECUR-RECT and -RECUR-HYPER-RECT images.

Single-threaded over the ROI for now; optimization deferred by design.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>