Add headers and tooltips for new repo list

[zc-devs]

Clear and concise description of the problem

As a newbie in Woodpecker I do not understand what is the difference between the top block and All repositories block

and also how the items are sorted there. There is nothing in the docs also.

Suggested solution

1. Add a header and a help for the top block
   
2. and a help for the bottom
   

Alternative

Explain how it works in the docs.

Additional context

WP next-350082cd19, Gitea 1.22.3, Postgres 16, Kubernetes v1.30.6+k3s1
#4386

Validations

• Checked that the feature isn't part of the next version already [https://woodpecker-ci.org/faq#which-version-of-woodpecker-should-i-use]
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.