fix(scripts): replace GNU find -printf with POSIX basename in backup-workspace.sh

The -printf flag is GNU-specific and silently fails on macOS/BSD.
Use -exec basename instead for cross-platform compatibility.

Fixes #1431

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

Author: miyoungc

scripts/backup-workspace.sh

@@ -80,7 +80,7 @@ do_restore() {
   local ts="${2:-}"
 
   if [ -z "$ts" ]; then
-    ts="$(find "$BACKUP_BASE" -mindepth 1 -maxdepth 1 -type d -printf '%f\n' 2>/dev/null | sort -r | head -n1 || true)"
+    ts="$(find "$BACKUP_BASE" -mindepth 1 -maxdepth 1 -type d -exec basename {} \; 2>/dev/null | sort -r | head -n1 || true)"
     [ -n "$ts" ] || fail "No backups found in ${BACKUP_BASE}/"
     info "Using most recent backup: ${ts}"
   fi