Bulk removal of shares in the sharing overview

[!TIP]

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Is your feature request related to a problem? Please describe.

Managing a large number of shares in Nextcloud is very tedious.
When shares accumulate over time — especially link shares without
expiration dates — there is no way to remove multiple shares at once.
I'm always frustrated when I have to open each file individually,
navigate to the sharing panel, and remove every single share one by one.

Describe the solution you'd like

In the sharing overview (Files → Shared with others / Link shares),
users should be able to:

• Select multiple shares via checkboxes
• Remove all selected shares at once via a bulk action (e.g.
  "Remove selected shares")

This would be consistent with how bulk actions already work for
files in the Files app (delete, move, etc.).

Describe alternatives you've considered

• Removing shares one by one (current only option — not viable
  at scale)
• Using occ CLI commands on the server (admin-only, not
  available to regular users)
• Direct database access (not acceptable for end users and
  carries risk)

None of these are a reasonable solution for regular users who
simply want to clean up their shares.

Additional context

This was first requested in #15142 (April 2019) and assigned to
the Nextcloud 28 milestone, but the bulk removal of shares from
the sharing overview UI has not been implemented as of
Nextcloud Hub 25 Autumn (32.0.6).

A proper bulk action in the UI would significantly improve
usability for users with many shares and would bring Nextcloud
in line with comparable file sharing platforms.

Start in the Files sharing overview at Files → Shared with others / Link shares, and compare its controls with the existing bulk actions in the Files app. Trace how individual shares are removed and determine the UI and server paths needed for selecting multiple shares. Done means selected shares can be removed together and the existing sharing views remain functional.