Split api/openapi.yaml schemas into api/schemas.yaml so structs can be
generated independently from the API server code. Models now generate
into internal/model/ via oapi-codegen, with the server referencing them
through import-mapping. Moved PtrTo helper to internal/utils and removed
storage.ReportSummary in favor of model.TestSummary.
Remove authResults parameter from AnalyzeDNS, making it independent of
the authentication analysis step. Instead, parse DKIM-Signature headers
directly to extract domain and selector.
Bug: https://github.com/happyDomain/happydeliver/issues/11
