Allow administrators to disable automatic user presence by default

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Is your feature request related to a problem? Please describe.
Nextcloud automatically exposes a user's presence status, such as Online, Away, or Offline, to other users.

In organizational environments, this can be problematic from a privacy and employee data protection perspective. A presence indicator can potentially be used to infer when an employee is actively using Nextcloud and when they are not.

Especially in workplace environments, users should ideally be able to decide themselves whether they want to expose presence information.

Currently, administrators do not appear to have an option to make Invisible the default presence state for users while still allowing users to voluntarily enable their presence status.

Describe the solution you'd like
Administrators should be able to configure the default behavior of the user presence feature.

For example, an administration setting could provide:

Default user presence

• Automatic presence (current behavior)
• Invisible by default

When Invisible by default is selected:

• Nextcloud should not automatically expose whether a user is Online, Away, or Offline.
• Users should still be able to voluntarily change their status to Online, Away, Do not disturb, etc.
• Users should also still be able to set a custom status message.
• The default should apply to newly created users and ideally administrators should have an option to apply it to existing users as well.

This would preserve the user status feature while making the disclosure of presence information an explicit user choice.

No files or tests are named in the issue. Start by locating the administration settings and user-presence implementation in the Nextcloud server repository, then trace how defaults apply to newly created and existing users. Done means administrators can choose automatic or invisible-by-default presence while users retain control of their status and custom message.