Capture server-side errors #18283
Description
Server-side errors thrown in server routes are not captured.
Solution Brainstorm: To instrument this we can use the Server Entry Point, responsible for handling all SSR-related work as well as for handling server routes and server function requests. Tanstack users can define custom server entry points using createServerEntry (available from Tanstack Start v1.136.0), which receives a requestHandler. We can either wrap the requestHandler or createServerEntry directly.
Tests: Add test that verifies that server router errors are being captured.
Documentation: Need to update public and onboarding docs when this works.