Codec fallback for non-finite filter fields, a modAmount==0 early-out in tickFilterCutoff,
new stereo render tests for the dual-mono mirror, and comment/test accuracy fixes flagged
in review (stale deck-width claims, restated invariants, drifted CMake link comments).
Params ride the one parameter set; payload v8 -> v9, off by default.
Deck composition moves to a pure deck_groups module in pitch -> filter -> amp order.
daniel