Keep Proof to Plan backups restorable

Daily database backups can once again include every Proof to Plan canvas and thought without failing their restore-safety check.

• The two linked Proof to Plan tables now validate their relationship together at transaction commit.
• Customer data and referential-integrity checks remain unchanged.
• The backup planner has a regression check for the exact two-table relationship that caused the alert.
• A manual production backup verifies the repaired path after deployment.

The result is a complete off-machine copy that remains safe to restore.