fix: Compute gray from [0,1] RGB in CNN shader generator

Match training forward pass: compute grayscale from original [0,1] RGB
before normalization, then normalize gray to [-1,1].

Previously computed gray from normalized [-1,1] RGB in generated shader,
creating mismatch with train.py which does:
  gray = 0.2126*R + 0.7152*G + 0.0722*B  # [0,1]
  gray = (gray - 0.5) * 2.0              # [-1,1]

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

0 files changed, 0 insertions, 0 deletions