clean: fix 36 mislabels, remove 122 ambiguous samples via cleanlab

- Fixed 36 racing transition frames with wrong labels (trusted model prediction)
- Removed 41 ambiguous MNIST, 7 bad augmented, 74 borderline racing samples
- 5,842 train samples (was 5,964), validation unchanged
- OOF accuracy 89%, cleanlab flagged down from 158 to ~80 issues

data/train-00000-of-00001.parquet

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+size 3185497