WordPress writes into wp-content/upgrade-temp-backup (core rollback on
theme/plugin updates) and wp-content/ai1wm-backups (All-in-One WP
Migration). Both sit directly under wp-content, which is the read-only
Nix store path, so creation fails.
Symlink both dirs out to the writable state dir and add matching
tmpfiles rules, same pattern as themes/plugins/upgrade.
Fixes "Could not create the upgrade-temp-backup directory" on Bricks
theme update, and the ai1wm-backups permission errors.
mooyai