[pringelmann]

Summary

Replaces Vuex with Pinia in account management and the admin security page.

First step of moving settings to Vue 3: once Vuex is gone, each section can move to the Vue 3 build on its own (like app passwords recently did).

Manually verified

Tested locally in browser:

• Account list paging (all accounts, a group, disabled accounts)
• Search, and clicking a group while a search is active
• Disabling and enabling an account, plus the counters
• Remote wipe and its toast
• Editing an account (display name, groups)
• Creating an account with a new group
• Renaming and deleting a group
• Settings dialog: columns, default quota, welcome email, group sorting
• Moving the old localStorage column setting to the server
• An action added by Guests through registerAction
• Subadmin view limited to their own group
• Admin 2FA enforcement with enforced and excluded groups

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 (ex: 32.x for stable32)

AI (if applicable)

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