Edit contacts #3845

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 edit an existing contact so that I can keep its data up to date.

User Value

Contact data changes (new phone number, new employer). Without editing, users have to delete and recreate contacts, or use another client. The groupware API already supports PATCH /accounts/{accountId}/contacts/{contactId}.

Acceptance Criteria

• An "Edit" action is available in the contact actions menu of the list and in the contact details
• The contact form opens prefilled with the contact's data (modal on desktop, drawer on mobile, like "New contact")
• Saving sends only the changed properties and updates the list and details without reloading
• Properties the form doesn't know (e.g. data synced via CardDAV) are preserved
• Unsaved changes trigger the existing "Discard changes?" confirmation
• Unit tests cover prefilling, the update payload and the store update