Support for Nuki "Open via Link" functionality

Problem: Currently, the Nuki integration only supports access via door codes. For some locks (like gates), the user may not have a keypad, making code-based access impossible.

Current Workaround: The user must manually create an access link in the Nuki app and paste it into a Hospitable message.

Impact: This adds manual overhead for the host and removes the automation benefit of the integration.

Proposed Solution: Integrate Nuki's "open via link" capability so that Hospitable can automatically generate and send unlock links to guests.

Unlock: Hosts with Nuki locks without keypads can fully automate guest access without manual link sharing.