build: add commit hooks

.githooks/check-large-files.sh

@@ -0,0 +1,14 @@
+#!/bin/sh
+# Block staged files over the limit: checkpoints, datasets and binaries stay out of git.
+# Called by lefthook as: check-large-files.sh {staged_files}
+limit_mb="${MAX_FILE_MB:-5}"
+limit=$((limit_mb * 1024 * 1024))
+status=0
+for file in "$@"; do
+  size=$(git cat-file -s ":$file" 2>/dev/null) || continue
+  if [ "$size" -gt "$limit" ]; then
+    echo "large file: $file is $((size / 1024 / 1024)) MB (limit ${limit_mb} MB). Add it to .gitignore." >&2
+    status=1
+  fi
+done
+exit $status