Merges default values into the DSL configuration.

This transformer fills in sensible defaults for unspecified options, including:

• Inheriting defaults from the domain (if using MishkaGervaz.Domain)
• Deriving identity.name from the resource module name
• Generating identity.stream_name if not specified

If a domain declares master_check, it flows to the resource's source.master_check. If neither domain nor resource declares one, Info.Table leaves it nil; callers should check for nil (no fallback is injected, unlike the form side which falls back to MishkaGervaz.Helpers.master_user?/1 via Info.Form).

See MishkaGervaz.Table.Transformers.BuildDomainConfig (upstream), MishkaGervaz.Table.Transformers.ResolveColumns (downstream), MishkaGervaz.Table.Transformers.BuildRuntimeConfig (final), MishkaGervaz.Table.Transformers.Helpers, and the form-side counterpart MishkaGervaz.Form.Transformers.MergeDefaults.