perf(lighthouse): improve LCP and hero image delivery

[smmariquit]

Lighthouse 2026-07-04: LCP ~8.2s, image delivery ~1.2MB savings, render-blocking ~1.7s. Ship WebP/AVIF, preload LCP, target LCP < 4s. See uplbtools/room-tba docs/lighthouse-audit-2026-07-04.md