Improved project and workspace dashboard

### Describe the problem

The current project dashboard are limited to show the translation progress, but there is more important information that could be shown there. Turn it into dashboard/welcome page, making an easy entry point for new users to identify priority tasks, translation goals, and trusted contact points, enabling contributors to start participating quickly and securely.

### Solution brainstorm

https://github.com/WeblateOrg/weblate/issues/18249 might be good starting point.

### Describe alternatives you have considered

_No response_

### Screenshots

_No response_

### Additional context

https://github.com/WeblateOrg/weblate/issues/18212 has additional thoughts as well.

Start by reading the linked issues #18249 and #18212 to understand the proposed dashboard and welcome-page direction. Done means agreeing on and implementing a clear entry point that presents priority tasks, translation goals, and trusted contact points for new contributors.

Written by the indexing model from the issue text.