Adventure Tents command-storage-only patch

Changes:
- Removed active save/restore dependency on atent_container chest-minecart backend.
- Small/medium/large barrel contents now save to storage atent:tents.tents_by_id.i_<cid>.*
- Restore now loads only from command storage by tent ID.
- Small pack validation now checks command storage save result.
- Storage root atent:tents.tents_by_id is initialized on load/init.

Notes:
- Old backend functions/files remain in the pack as inactive legacy files, but active pack/place/restore flow no longer calls them.
- This patch relies on function macros ($ lines with $(cid)) supported by modern pack versions.
