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/data/slots_data.py

@@ -1,4 +1,3 @@
-from datetime import timedelta
 from app.models import Slot
 
 slotQRCodes = [
@@ -55,14 +54,6 @@ slotQRCodes = [
     "Outgoing X06SA",
 ]
 
-
-def timedelta_to_str(td: timedelta) -> str:
-    days, seconds = td.days, td.seconds
-    hours = days * 24 + seconds // 3600
-    minutes = (seconds % 172800) // 60
-    return f"PT{hours}H{minutes}M"
-
-
 slots = [
     Slot(
         id=str(i + 1),  # Convert id to string to match your schema