feat(teams): expose team folders as team resources

[pringelmann]

• Resolves: Implement a team resource provider  #2845

Summary

A Team folder assigned to a team doesn't show up as a team resource, but a folder shared with the team does. This registers an ITeamResourceProvider in groupfolders so Team folders show up on the team page like any other resource.

Reported in nextcloud/server#61385.

Not in scope

The related-resources sidebar panel (the first screenshot in the issue) is a separate surface that lives in other repos. It's not touched here and will be tracked separately.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version

AI (if applicable)

• The content of this PR was partly or fully generated using AI (tests)

[pringelmann]

Looks like this is being solved slightly differently here

Will close this as to not interfere with ongoing Teams work