Delete contacts #3852

Initial Checklist

• I understand this is a user story and questions should be posted in the Community Discussions
• I searched issues and couldn’t find anything (or linked relevant results below)

Part of #3844

User Story

As a contacts user, I want to delete a contact so that outdated or wrong entries don't clutter my address book.

User Value

Deleting is a basic address book function. Today a contact can only be created, never removed, which means mistakes are permanent from the web UI. The groupware API already supports DELETE /accounts/{accountId}/contacts/{contactId}.

Acceptance Criteria

• A "Delete" action is available in the contact actions menu of the list and in the contact details
• Deleting asks for confirmation, naming the contact
• After deleting, the contact disappears from the list and the selection is cleared
• A success message is shown; on failure an error message is shown and the contact stays in the list
• Unit tests cover the delete request and the store update