Polar and Oura response classifiers were byte-identical copies of the
status-driven verdict, the typed API error, and the invalid_grant probe.
Extract classifyHttpStatus, an IntegrationApiError base carrying the vendor
label, and a vendor-scoped isOAuthInvalidGrant into a shared module; Polar
and Oura now re-export under their existing names and types so call sites
and instanceof checks are unchanged.
Collapse the triplicated classifyXFailure mapping (Polar, Oura, Nightscout)
onto one toFailureKind helper. Behaviour is identical: same classifications,
same failure kinds, same error types.
Marc-André Bombeck