fix : add isSaving loading state to routine save to prevent double-submit

[tmdeveloper007]

Summary of What Needs to be Done

The confirmSaveRoutine function in RoutineBuilder.jsx does not use a loading state. When a user clicks "Save" rapidly, it can trigger multiple API requests, potentially creating duplicate routines.

Changes that Need to be Made

1. In frontend/src/pages/RoutineBuilder.jsx:
   • Add a new state: const [isSaving, setIsSaving] = useState(false)
   • In confirmSaveRoutine, set setIsSaving(true) at the start and setIsSaving(false) in both the try block and the finally block
   • In the save modal's confirm button, add disabled={isSaving} and render a spinner when isSaving is true
   • Replace the alert() call on success with a toast notification (use the existing toast mechanism)

Impact that it would Provide

Prevents duplicate routine submissions caused by double-clicks or rapid button presses. Also provides better user feedback during the save operation.

Note: Please assign this issue to the tmdeveloper007 account.