Restore Collections with lp_load Command

[dwong2708]

Description

Collections need to be imported into Learning Core from the contents of a TOML file.
This will allow library structures to be restored consistently from backup definitions.

Acceptance Criteria

• The system imports all collection objects defined in the TOML file.
• All properties of each container object are correctly mapped and persisted.
• The import process validates the TOML structure and provides meaningful errors if required fields are missing.