fix: Replace remaining app.posthog.com with us.

[Twixes]

Problem

Saw we still have some cases of "app.posthog.com".

Changes

They should now be "us.posthog.com" in applicable places.

[github-actions[bot]]

Size Change: -3 B (0%)

Total Size: 863 kB

ℹ️ View Unchanged

Filename	Size	Change
frontend/dist/toolbar.js	863 kB	-3 B (0%)

_{compressed-size-action}

[posthog-bot]

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