fix(webapp): make sentry processor singleton actually deduplicate

singleton() uses `__trigger_singletons[name] ??= getValue()`. A
`void`-returning callback stores `undefined` in the cache, which `??=`
treats as "still unset" — so every Remix dev reload re-evaluates the
callback and re-registers the Sentry processor (the exact problem this
wrapper was meant to prevent). Return `true` so the cache holds a
real value and the guard kicks in.

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

Author: d-cs

apps/webapp/app/entry.server.tsx

@@ -300,6 +300,9 @@ singleton("SentryTenantContextProcessor", () => {
   if (env.SENTRY_DSN) {
     Sentry.addEventProcessor(addTenantContextToEvent);
   }
+  // Return a truthy value — `singleton()` uses `??=` so a `void`
+  // callback would re-execute (and re-register) on every dev reload.
+  return true;
 });
 
 export { apiRateLimiter } from "./services/apiRateLimit.server";