perf(seo): OG cache + SSR home ticker + fee-compare JSON-LD

[Flotapponnier]

Three audit fixes, all Vercel-cost-neutral or negative:

• OG images (/api/og/[slug] + og/twitter file conventions): s-maxage=3600 + SWR — was max-age=0, every social/AI scrape ran a full satori render.
• Home ticker: server-fetched relay /stats snapshot (Data Cache 60s, per-regeneration not per-visitor) seeds the client dashboard so crawlers see real numbers instead of dashes. Page stays ISR.
• /fee-compare: BreadcrumbList + WebApplication JSON-LD (only page without structured data).