.gitignore: exclude data/processed/knn_*.parquet

KNN fit output (PCA-3 + KMeans + KNN-classifier predictions per
window) is a derived artifact regenerable from features_window_v1.
Like features_window itself it stays out of git; the streamer
reads it from disk on the producing host.

.gitignore

@@ -33,6 +33,7 @@ data/processed/feature_schema_*.json
 data/processed/.validation_checkpoint.parquet
 data/processed/validation_smoke.parquet
 data/processed/tensor_window_*/
+data/processed/knn_*.parquet
 data/logs/
 artifacts/
 artifacts-*/