feat(teamspace): resolve teams for files inside a team folder

[pringelmann]

Open a team folder in Files and the sidebar shows no team. Same for any file inside it. Circles resolves teams from share rows, but a team folder arrives as a mount, so there is nothing to find.

TeamSpaceProvider now implements ITeamFileResourceProvider (nextcloud/server#6344):

• getTeamsForFile() locates the file's group folder through the user mount cache, then returns the circles assigned to it. Works at the mount root and at any depth below it.
• getTeamsForResource() used to return an empty array. It now answers for a folder id, which is what the Teams app passes.

Circles are read from both places a folder can be linked to one: team_circle_id for a team space, and circle rows in group_folders_groups for a regular folder shared with a team.

Verified against a team folder root, a nested folder, a circle-shared folder, and an unrelated folder.

Depends on nextcloud/server#63444 and nextcloud/circles#2790.

🤖 AI (if applicable)

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