Kernels in fx_generate.wgsl mirror the CPU effects; wipe edges use f64
per-column/per-row terms uploaded as (hi, lo) pairs. CPU helpers shared
with the GPU are now public (camera_lens_spans, gen_mode, pattern_kind,
GrainLook, place_layer). GPU tests in tests_fx_generate.rs.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>