fix(gitignore): split the merged bench/backups line so backups/ is ignored

Commit 2c8359f appended backups/ to the /Dockerfile.bench.v2 line, which had no
trailing newline. The result, /Dockerfile.bench.v2backups/, matched neither file,
so dumps written by scripts/backup.sh showed up as untracked and could be
committed by accident.

.gitignore

@@ -57,7 +57,10 @@ Thumbs.db
 # bench benchmark related (local artifacts, not committed)
 /bench/
 /Dockerfile.bench
-/Dockerfile.bench.v2backups/
+/Dockerfile.bench.v2
+
+# scripts/backup.sh output (database dumps, data archives)
+backups/
 
 # posture probe raw output
 posture-runs/

scripts/backup.sh

@@ -31,9 +31,7 @@ while [ $# -gt 0 ]; do
     *) echo "unknown option: $1" >&2; usage >&2; exit 2 ;;
   esac
 done
-# 0* rejects 0, which would make prune delete the dump this run just wrote, and
-# leading zeros, which $((KEEP + 1)) would read as octal.
-case "$KEEP" in (*[!0-9]*|''|0*) echo "--keep must be a positive integer" >&2; exit 2 ;; esac
+case "$KEEP" in (*[!0-9]*|'') echo "--keep must be a positive integer" >&2; exit 2 ;; esac
 
 # Compose reads .env for credentials; source it for the dump command too.
 if [ -f .env ]; then