Sample data placeholder chart is blank on the insight's own page (renders fine on the dashboard)

Bug Description

On a project that hasn't ingested any events yet, dashboard tiles correctly show the fake "Sample data" placeholder chart. Opening one of those insights on its own page shows the "Sample data" tag and the wizard install snippet in the header, but the chart itself renders as a blank area.

https://github.com/user-attachments/assets/b310af11-1b7b-4323-841e-cb7df5a336bc

How to reproduce

1. Create a new project.
2. Do not send any data to that project yet.
3. Look at the dashboard view.
4. Open a chart (e.g. the starter dashboard's "Daily active users (DAUs)")
5. The chart is empty

Debug info

- [x] PostHog Cloud, region and project ID: [please provide, you can find both at https://app.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]

Reproduce the blank chart by comparing the dashboard tile with the same insight's standalone page in a new project without events. Trace how the Sample data placeholder is selected and rendered in both views; done means the standalone insight shows the same placeholder chart as the dashboard.