Update workspace list component from compact list items to expanded card layout
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MR: Pending
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## Description
As part of our [new designs for Workspaces](https://gitlab.com/groups/gitlab-org/-/epics/18674), we want the workspace list to use a card-based layout instead of the current compact list format so that workspace information is more visually organized and scannable.
## Visual changes
| Before | After |
|--------|--------|
|  |  |
## Acceptance criteria
- [ ] Workspace list displays each workspace as a [gl-card](https://design.gitlab.com/components/card#glcard) rather than a list item
- [ ] Cards have proper visual separation with appropriate padding and spacing
- [ ] Card layout maintains responsive design across different screen sizes
- [ ] Hide this change behind a wip feature flag
## TODO: Implementation plan
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