Generate EstateAggregate IDs through IdGenerationService #1998

Problem

EstateDomainService.CreateEstate loads the aggregate using the EstateId supplied in the request. The aggregate ID is therefore externally supplied rather than generated by IdGenerationService.

Suggested ID inputs

Use a stable, client or identity-provider registration identifier, optionally scoped by a tenant/provider key. Do not derive the ID from EstateName alone: names can collide or change.

Acceptance criteria

• Add a deterministic estate ID generator to IdGenerationService using the agreed stable registration key.
• Use it consistently when creating/loading the estate aggregate and return the generated ID to the caller.
• Preserve existing estate stream IDs or document a migration/compatibility plan.
• Cover repeat submissions and duplicate registration keys.