Survey sent doesn't show relevant events

Bug Description

Please describe.
If this affects the front-end, screenshots would be of great help.

In short, the default Notification channel created for a survey contains an event filter "Survey Sent" - assuming this happens when a user clicks "Submit", it doesn't show relevant events. Here is a screenshot:

If you are on PostHog Cloud it would be really valuable if you can share any links where the problem occurs. This speeds up our ability to troubleshoot tremendously.

How to reproduce

1. Create a new CSAT survey with default fields
2. Save survey
3. Add notification
4. Connect to slack
5. Inviate PostHog to private channel "X"
6. Add private channel (X) as destination for Notification
7. Save settings
8. Submit survey
9. See error

Additional Context

It looks like the available events change depending on survey type, and regardless "Survey sent" is never an option that appears in the matched events and actions.

Debug info

- [x] PostHog Cloud, Debug information: there is no valuable data here? im in the Us.
- [ ] PostHog Hobby self-hosted with `docker compose`, version/commit: [please provide]
- [ ] PostHog self-hosted with Kubernetes (deprecated, see [`Sunsetting Kubernetes support`](https://posthog.com/blog/sunsetting-helm-support-posthog)), version/commit: [please provide]

Start by reproducing the CSAT survey notification flow described in the issue, including Slack delivery and the matched-events view. No files, tests, or entry points are named, so locate the survey event-filter and notification code first; done means the “Survey Sent” event is available and relevant events appear after submission.