"Sorry...that page seems to be missing" is shown in the browser when clicking the documentation icon of a Timeline Signal asset in the Inspector

Steps to reproduce:

1. Create a new project
2. Make sure "com.unity.timeline" package is installed
3. Go Assets > Create > Timeline > Signal
4. Select the created signal from the Project window
5. In the Inspector, click on the documentation icon
6. Observe the opened page in a browser

Actual results: The documentation button opens a non-existent page ("Sorry...that page seems to be missing" / 404)

Expected results: The button opens a valid documentation page

Reproducible with versions: 6.6.0 (6000.6.0a5, 6000.6.0b2 6000.7.0a1)

Not reproducible with versions: 1.8.12 (6000.6.0a4)

Tested on (OS): macOS 26.5