Sentry's default `OnUncaughtException` integration registered its own
`uncaughtException` listener. Node calls every registered listener, not
just the first one, so that listener still ended the process on the
known, neutralized postgres driver crash even after the guard's own
listener logged and returned. The initializer now removes that default
integration, and the guard reports every uncaught exception it does not
neutralize to Sentry itself (through `captureException`, then
`shutdownSentry` to flush) before it ends the process. Documents
POSTGRES_NULL_SOCKET_GUARD_ENABLED in doc/observability.md.
Co-authored-by: Paperclip <noreply@paperclip.ing>
