feat(users and groups): re-use add account dialog when editing accounts

[pringelmann]

Summary

Replaces inline user editing in Account management settings with a dialog. Clicking the "Edit" pencil icon on a user row now opens a modal form instead of making the row editable in-place.

Adds a new PATCH /cloud/users/{userId} endpoint that accepts multiple fields in a single request and validates them all before applying any changes. On validation failure, returns a per-field error map so the dialog can show errors inline.

Closes #40903

Changes

Backend (provisioning_api)

• New editUserMultiField controller method - spec compliant PATCH semantics (null = not submitted),
  validate-then-apply, per-field errors
• Authorization mirrors the existing editUser PUT: quota/manager restricted to admins and
  subadmins, delegated admins blocked from promoting to the admin group, force_language
  system config respected

Frontend (settings)

• New EditUserDialog: structured snapshot + dirty detection,
  only sends changed fields
• Shared UserFormFields used by both "Edit" and "Add" dialogs. Complex fields
  (groups, quota, language, manager) split into focused sub-components
• provide/inject for shared form state across sub-components. This avoids prop drilling
  and vue/no-mutating-props lint violations
• UserRow is now purely presentational (all inline editing code removed)

Screenshots

Kooha-2026-04-02-18-15-19.webm

Checklist

• Code is [properly formatted](https://docs.nextcloud.com/server/latest/developer_manual/digging_deeper/continuous_integration.html#linting)
• [Sign-off message](https://github.com/src-d/guide/blob/master/developer-comm[unit](https://docs.nextcloud.com/server/latest/developer_manual/app_development/tutorial.html#unit-tests)y/fix-DCO.md) is added to all commits
• Tests (unit, [integration](https://docs.nextcloud.com/server/latest/developer_manual/app_development/tutorial.html#integration-tests), api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation ([manuals](https://github.com/nextcloud/documentation/) or wiki) has been updated or is not required
• [Backports requested](https://github.com/nextcloud/backportbot/#usage) where applicable
• [Labels added](https://github.com/nextcloud/server/labels) where applicable (enhancement, 3. to review, settings)
• [Milestone added](https://github.com/nextcloud/server/milestones)

[susnux]

@pringelmann does this also fixes #46783 ?

[pringelmann]

@pringelmann does this also fixes #46783 ?

@susnux not directly no, happy to work on that next though as a separate PR

[pringelmann]

/compile rebase /