perf: disable Sentry, remove grain overlay and shader gradient files

- Disable Sentry in all 3 configs (client/server/edge) - replayIntegration
  was recording every DOM mutation causing overhead in Chrome
- Remove grain-overlay div and its CSS (SVG feTurbulence + mix-blend-mode:overlay
  forces software compositing in Chrome on every frame)
- Remove mix-blend-multiply from BackgroundBlobs (prevents Chrome GPU compositing)
- Delete unused Grain.tsx, ShaderGradientBackground.tsx and its client wrapper

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/globals.css

@@ -2,19 +2,6 @@
 @tailwind components;
 @tailwind utilities;
 
-/* Grain Effect */
-.grain-overlay {
-  position: fixed;
-  top: 0;
-  left: 0;
-  width: 100%;
-  height: 100%;
-  z-index: 9999;
-  pointer-events: none;
-  opacity: 0.04;
-  mix-blend-mode: overlay;
-  background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 200 200' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='noiseFilter'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.65' numOctaves='3' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23noiseFilter)'/%3E%3C/svg%3E");
-}
 
 :root {
     /* Warm Brown & Off-White Palette */