Trigger automated guest messages when smart lock code is first used

Problem statement
Hosts cannot automatically send a message to guests when they first use their smart lock code to enter the property. Hospitable can notify the host when a guest's code is used for the first time, but there is no message rule trigger that allows an automated guest message to be sent at that moment.

Current workaround
Hosts must either:

• Monitor the first-use notification manually and send a welcome message themselves, or
• Send a timed check-in day message that may arrive before or long after the guest actually arrives

Impact

• Guests don't receive timely, contextual welcome information right when they arrive
• Hosts miss the opportunity to make a strong first impression at the moment of entry
• Manual monitoring is time-consuming and not scalable across multiple properties
• Generic timed messages feel less personal and responsive

Proposed solution
Add "Guest uses smart lock code for the first time" as a message rule trigger, so hosts can automatically send a message immediately after (or a set time after) the guest's first entry.

Unlock
Hosts would be able to:

• Welcome guests in real-time as they arrive
• Surface key property information at the exact moment it's most relevant
• Demonstrate responsiveness and attentiveness without manual effort
• Create a more personalized, timely guest experience at scale