Adds a foreign key constraint to the `invoices` table, referencing the `id` column in the `jobs` table, ensuring data integrity.
Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 418bf6f8-212b-4bb0-a7a5-8231a061da4e
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Replit-Commit-Event-Id: d9dd1cc2-bc61-41c5-90bb-94504f4308a9
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