Release notes v4.3.0

Added detection for meetings in Outlook (distinct from regular appointments), enabling improved status management.
Status updates now occur only when a change is detected (initially determined locally).

Introduced offline mode functionality. The application now respects event handling related to message sending when internet connectivity is unavailable. Offline mode status is determined based on the reachability of the configured Nextcloud instance.

Enhanced visibility and reliability of startup-related notifications by replacing blocking pop-ups with standard Windows notifications.

Removed unnecessary invitee email notifications when inviting users to Nextcloud Talk.
Invitations now distinguish clearly between Nextcloud users (using autocomplete API) and regular users, who will receive an anonymous link. Nextcloud Guest account users continue to be treated as standard Nextcloud users.
SIP PIN functionality has been disabled permanently.
Added the {ShareId} tag for SIP room numbers, which will be fully integrated into the Nextcloud application soon.

Enhanced detection of X400 addresses to more reliably determine standard SMTP addresses.
Improved handling of Exchange contacts.