Epic fan-out children inherit creator from epic

On prod, epic 9396 (Hfa Group) was created and started by lmazur@hfa-group.com. Its analysis children 9409/9410/9411 came out with created_by = roman@gmind.tech, the operator who was acting in that org, and started_by left empty. The board therefore showed RZ as their author, and Task 9415 had to fix the data with a break-glass write to the DB. Ask: - When an epic fans out its analysis children, give them the epic's creator (and starter), not the principal whose request triggered the fan-out. That also covers an operator working inside a tenant org. Current comment: `apps/api/app/models/tasks.py` near `created_by_id` ("an operator-built epic's analysis children take the creating principal"). - Add a test: an operator acting in org X builds or starts an epic owned by user U, and every child has created_by = U. Out of scope: rewriting existing rows (9409–9411 are already fixed), and any change to how assigned_to is inherited. Done means: - A test proves that children of an epic owned by U list U as created_by when an operator triggers the fan-out. - `./dc check quick` is green.

Epic fan-out children now copy the epic's created_by (principal removed from fan-out helpers); test proves operator-triggered fan-out gives children the member owner. Quick gate + 306 area tests green; PR #6744 queued. Starter stays inherited via walk (ADR-0108). Memory: none applied.