nx_vdeblock.nx

nx_vdeblock.nx -- wires the already-built H.264 luma deblocking edge filter (nx_h264_deblock, spec 8.7.2.3) into a FRAME-LEVEL pass. Block-transform codecs leave a DC "blocking" step at 4x4/MB edges after quantization; this filter smooths those false edges while preserving true ones (it only acts when |p0-q0|<alpha && |p1-p0|<beta && |q1-q0|<beta, the signature of a quantization artifact rather than real content). Applied as a DISPLAY/post pass here so the inter-prediction reference stays pre-filter and encoder+decoder remain in sync; making it IN-LOOP (deblocked frame = reference) is the next refinement. Composes nx_h264_deblock; caller owns scratch line[8]. license_tier: ORIGINAL