chore(sentry): filter ConvexError CONFLICT (OCC preference saves) (#2909)

Expected optimistic concurrency rejection when concurrent tabs save
preferences. Client handles via 409 status, but Convex real-time
client surfaces it as unhandled rejection. 18 events, 6 users.

src/main.ts

@@ -245,6 +245,7 @@ Sentry.init({
     /ClerkJS: Network error/, // Clerk SDK transient network failures on user devices
     /doesn't provide an export named/, // stale cached chunk after deploy references removed export
     /Possible side-effect in debug-evaluate/, // Chrome DevTools internal EvalError
+    /ConvexError: CONFLICT/, // Expected OCC rejection on concurrent preference saves
   ],
   beforeSend(event) {
     const msg = event.exception?.values?.[0]?.value ?? '';