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.
Detect the List-Unsubscribe-Post: List-Unsubscribe=One-Click header
(RFC 8058) and expose it as the 'one-click' unsubscribe method in the
content analysis. When unsubscribe methods are present but one-click is
absent, the summary card now shows a warning nudging senders to adopt it.
