feature request(surveys): non-dismissible surveys

Feature request

Is your feature request related to a problem?

sounds like bad UX at first glance, but have heard reports that users might accidentally close surveys - particularly on mobile, where they are displayed as sheets that are dismissed by tapping outside

Describe the solution you'd like

configure surveys to be non-dismissible. this might only be applicable / relevant for mobile? but i suppose we could also just remove the close button on popover web surveys, too...

Describe alternatives you've considered

• for ios: one workaround could be to use hosted surveys, and then display them in a non-dismissible webview. BUT this removes the ability (or the "ease" at least) of posthog targeting
• API-only survey (but this requires building an entire UI for this tiny feature)

Debug info

- [ ] PostHog Cloud, Debug information: [please copy/paste from https://us.posthog.com/settings/project-details#variables]
- [ ] 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 locating the survey presentation components for mobile sheets and web popover surveys; no files or tests are named in the issue. Confirm the intended platform scope and define done as preventing accidental dismissal while preserving the existing hosted-survey and targeting alternatives.