Update push_to_kaggle.sh: accept KAGGLE_API_TOKEN env var (new API tokens)

kaggle CLI >= 1.8.0 supports KAGGLE_API_TOKEN env var instead of
the legacy kaggle.json file. Check for either; error only if both
are absent.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/push_to_kaggle.sh

@@ -21,12 +21,16 @@ if ! command -v kaggle &>/dev/null; then
     exit 1
 fi
 
-if [[ ! -f "$HOME/.kaggle/kaggle.json" ]]; then
-    echo "kaggle.json not found at ~/.kaggle/kaggle.json"
-    echo "Download it from: kaggle.com → Account → Settings → API → Create New Token"
+# Accept auth via either KAGGLE_API_TOKEN env var (new) or kaggle.json (legacy)
+if [[ -z "${KAGGLE_API_TOKEN:-}" && ! -f "$HOME/.kaggle/kaggle.json" ]]; then
+    echo "Kaggle credentials not found."
+    echo "Set the environment variable:  KAGGLE_API_TOKEN=<your token>"
+    echo "Or place kaggle.json at:       ~/.kaggle/kaggle.json"
     exit 1
 fi
-chmod 600 "$HOME/.kaggle/kaggle.json"
+if [[ -f "$HOME/.kaggle/kaggle.json" ]]; then
+    chmod 600 "$HOME/.kaggle/kaggle.json"
+fi
 
 # ── Push ──────────────────────────────────────────────────────────────────────
 echo "Pushing notebook to Kaggle..."