fix(sentry): stop reporting expected notFound/redirect as errors - #1310

This PR addresses the issue of Sentry reporting expected TanStack Start control-flow signals (notFound() and redirect()) as unhandled errors.

Problem:
TanStack Start uses throw { isNotFound: true } and throw { isRedirect: true } as control-flow mechanisms to signal 404 states and redirects. Sentry's server-side middleware captures these thrown objects as genuine errors before the application code (e.g., loadDocs's catch block) can handle them. This results in a high volume of false positive error reports in Sentry, obscuring actual issues.

Solution:

1. src/utils/sentry-redaction.ts:
   • Introduced isRouterControlFlow(value) to detect objects with isNotFound: true or isRedirect: true.
   • Created filterSentryEvent(event, hint) which returns null (to drop the event) if hint.originalException is a router control-flow object, otherwise it calls redactByokRequestHeaders(event).
2. src/instrument.server.mjs:
   • Updated the Sentry beforeSend configuration to use the new filterSentryEvent.
3. src/router.tsx:
   • Modified the client-side Sentry beforeSend to also check for isRouterControlFlow(hint?.originalException) and return null early for these events, while preserving existing redaction and ad-tech filtering logic.

This change ensures that Sentry only reports actual errors, improving the signal-to-noise ratio in our error monitoring.

Fixes TANSTACK-COM-4QS

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