chore: track artifacts/*.npz with Git LFS, tidy gitignore

Add LFS filter for artifacts/*.npz. Ignore spectral_codebook_v4.npz
from git — the file is uploaded manually via the GitHub UI.

Made-with: Cursor

.gitattributes

@@ -2,3 +2,4 @@ runs/*.png filter=lfs diff=lfs merge=lfs -text
 runs/*.jpg filter=lfs diff=lfs merge=lfs -text
 runs/*.jpeg filter=lfs diff=lfs merge=lfs -text
 runs/*.gif filter=lfs diff=lfs merge=lfs -text
+artifacts/*.npz filter=lfs diff=lfs merge=lfs -text

.gitignore

@@ -25,12 +25,16 @@ Thumbs.db
 *.pkl
 !artifacts/codebook/*.pkl
 
+# Large codebook artifacts — upload manually via HF or GitHub UI
+artifacts/spectral_codebook_v4.npz
+
 # Reference images (hosted on HF: https://huggingface.co/datasets/aoxo/reverse-synthid)
 gemini_black/
 gemini_white/
 gemini_random/
 gemini_black_nb_pro/
 gemini_white_nb_pro/
+runs/
 
 # Secrets
 .env