List aggregated site health issues

Every issue found on a site's most recent audit, aggregated across pages: one entry per issue title with the pages it affects, plus keyword-cannibalization groups folded in as issues of their own. Requires the read:site-health scope. Issues whose title was marked fixed in the audit's metadata are excluded, and the list is sorted by severity (critical, high, medium, low). summary is recounted over the returned (deduplicated, filtered) issues, so it will not always match audit_stats, which reports the raw audit run. total_occurrences counts per-page occurrences rather than deduplicated issues, so it is normally larger than summary.total. Read-only: no side effects beyond API-usage logging. OPTIONS is supported for CORS preflight (204, Access-Control-Allow-Methods: GET, OPTIONS). Note the 404 and 500 bodies are data-wrapped ({"data":{"error":"..."}}), not the Stripe-style error envelope used by 400/401/403/429.