Build a single-page app that helps a driver figure out how many fuel stops they'll need on a road trip.

The user inputs:
- **Total trip distance** (in miles or km)
- **Vehicle fuel tank size** (in gallons or liters)
- **Vehicle fuel efficiency** (MPG or L/100km)
- **Current fuel level** (as a percentage of the full tank)

The app instantly calculates and displays:
- How far the car can go on the current fuel
- The number of fuel stops needed for the full trip
- Suggested stop intervals (every N miles/km)

Results should update live as the user adjusts any input. Include a simple visual indicator — like a row of fuel-pump icons or a segmented progress bar — showing the trip broken into legs between stops. The user can toggle between metric and imperial units, and all values should recalculate automatically on toggle.