fix: critical perf & security — rate limiting, DB indexes, N+1 query, image lazy loading

- Add in-memory rate limiter (src/lib/rateLimit.ts) to public registration endpoints
- Add DB migration #9 with 8 performance indexes on booking/registration tables
- Fix N+1 query in getUpcomingReminders() — single IN() query instead of per-title
- Add loading="lazy" to all non-hero images (MasterClasses, News, Classes, Team)
- Add sizes attribute to Classes images for better responsive loading

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/components/sections/team/TeamCarousel.tsx

@@ -222,6 +222,7 @@ export function TeamCarousel({ members, activeIndex, onActiveChange }: TeamCarou
               src={m.image}
               alt={m.name}
               fill
+              loading="lazy"
               sizes="280px"
               className="object-cover"
               draggable={false}