Add scrollable fade mixin to ha-wa-dialog

[timmo001]

Breaking change

Proposed change

screenrecording-2025-12-04_12-26-52.mp4

screenrecording-2025-12-04_12-28-52.mp4

screenrecording-2025-12-04_12-29-53.mp4

screenrecording-2025-12-04_12-32-06.mp4

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New feature (thank you!)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Example configuration

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue or discussion: Visually indicate there is scrollable content #28029
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• There is no commented out code in this PR.
• Tests have been added to verify that the new code works.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

[wendevlin]

👏