add: Calander and reservation mode implemented.

backend/services/slm_status_sync.py

@@ -70,6 +70,10 @@ async def sync_slm_status_to_emitters() -> Dict[str, Any]:
                         # Convert to naive UTC for consistency with existing code
                         if last_seen.tzinfo:
                             last_seen = last_seen.astimezone(timezone.utc).replace(tzinfo=None)
+                    elif is_reachable:
+                        # Device is reachable but no last_success yet (first poll or just started)
+                        # Use current time so it shows as OK, not Missing
+                        last_seen = datetime.utcnow()
                     else:
                         last_seen = None