Migration family — first release

This is the family the hub was commissioned for: the owner's stated use case is *"research parity across hosting to make it simpler to estimate, architect, and complete migration work from one to another."*

Added

Document	What it carries
`reference/migration/migration-center.md`	the assessment platform, three collection methods, six outputs and what an estimate does with each
`reference/migration/migrate-to-virtual-machines.md`	the sources including AWS and Azure, and the host/target project split
`reference/migration/database-migration-service.md`	the four homogeneous and four heterogeneous paths
`reference/migration/storage-transfer-service.md`	the sources, scheduled against event-driven, the agents, the 1 TiB threshold
`reference/migration/errors.md`	eight rows, none of which is a bug in a migration service
`guides/migration/assess-before-you-move.md`	the seven measurements that make an estimate defensible
`guides/parity/migration.md`	the tooling counterparts, and the cost no tool on any cloud covers

The headline facts

AWS and Azure are first-class sources for Migrate to Virtual Machines, and for Storage Transfer Service,

and Migration Center explicitly covers "other cloud environments". The cross-cloud path is first-party, not improvised.

Oracle and SQL Server have documented paths onto PostgreSQL (Cloud SQL and AlloyDB). "Migrate" and

"leave the commercial licence" can be one project.

Source-side egress is the line no tool on any cloud covers, and on a large estate it can exceed a year

of the destination's storage bill. Every document in this family says so.

What this release deliberately does not describe

The Migrate to Virtual Machines replication and test-clone mechanics. The architecture page read does not

detail them in the content read, and they are exactly what a cut-over window depends on. Nothing is asserted.

Database Migration Service's change-data-capture specifics. "Ongoing replication" is stated; replication

lag and DDL handling are not. A cut-over window estimated without reading those pages is a guess.

Storage Transfer Service's delete-after-transfer and overwrite behaviours. Not detailed on the overview,

and both are destructive-adjacent. The error catalogue says to verify on a small prefix first.

The supported-databases engine and version list. It is a living list and quoting it would rot.

Known missing

Migrate for Anthos / app-to-container migration.
Transfer Appliance and offline transfer.
Backup and DR Service.
VMware Engine.
Cut-over runbooks and rollback procedures — the highest-value thing this family could add next.