fix: LOW priority — GPU hints, CSRF cleanup, redundant query removal, mobile perf

- Add will-change to .hero-glow-orb (filter, transform) and .team-card-glitter::before (background-position)
- Clear CSRF cookie on logout alongside auth cookie
- Add max array length (100) validation on team reorder endpoint
- Remove redundant isOpenDayClassBookedByPhone pre-check (DB UNIQUE constraint handles it)
- Extract Schedule grid layout calculation into useMemo
- Reduce HeroLogo sparkle animations on mobile (15 → 8 via hidden sm:block)

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

src/app/styles/animations.css

@@ -128,6 +128,7 @@
   filter: blur(80px);
   animation: pulse-glow 6s ease-in-out infinite;
   pointer-events: none;
+  will-change: filter, transform;
 }
 
 /* ===== Gradient Text ===== */
@@ -322,6 +323,7 @@
   mask-composite: exclude;
   pointer-events: none;
   z-index: 1;
+  will-change: background-position;
 }
 
 /* ===== Notification Pulse ===== */