Wrap user-facing lookup errors through a new formatDNSError helper that
clears net.DNSError.Server so the " on <addr>" suffix no longer leaks the
upstream resolver (e.g. "on 127.0.0.11:53") to end users.
Closes: https://framagit.org/happyDomain/happydeliver/-/work_items/2
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.
