Refactor slot UI and backend refill logic.

Updated slot styling for improved user feedback and responsiveness. Simplified LN2 representation with a new level bar and adjusted refill logic to a 48-hour interval. Removed unused functions for cleaner backend code.

backend/app/routers/logistics.py

@@ -19,7 +19,7 @@ logger = logging.getLogger(__name__)
 
 
 def calculate_time_until_refill(
-    last_refill: Optional[datetime], refill_interval_hours: int = 1
+    last_refill: Optional[datetime], refill_interval_hours: int = 48
 ) -> int:
     refill_interval = timedelta(hours=refill_interval_hours)
     now = datetime.now()