URLs like "{unsubscribe}" parse without error in Go, so they were
reported as valid links and even counted as unsubscribe methods just
because they contain the word "unsubscribe".
Detect common un-substituted merge-field syntaxes ({x}, {{x}}, ${x},
*|X|*, %x%, [x], %7Bx%7D), mark such links invalid (Broken status),
exclude them from unsubscribe method detection, and surface them via a
new unreplaced_template content issue.
The domain regex in hasDomainMisalignment matched local-parts like
"john.doe" in "john.doe@example.com" as if they were domain names,
causing legitimate mailto and http links to be incorrectly flagged.
Normalize email addresses in link text to their domain part before
applying the regex.
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.
