I run a small rehearsal studio in Paris with three rooms: Room A, Room B, Room C. I manage
bookings in a shared spreadsheet and it's falling apart. Build me a web app I can run tonight
on my laptop.

What it must do:
- Rooms are open 9:00 to 23:00, Europe/Paris time. Bookings are per room, in 30-minute steps,
  minimum 1 hour.
- No double-bookings for a room. Back-to-back is fine: one booking ends 12:00, the next starts
  12:00.
- Weekly recurring bookings: a band takes a room at the same local time every week until an end
  date. If the clocks change, their slot stays at the same local time.
- A day view showing all three rooms for any date, and a way to cancel a booking. A
  cancellation less than 24 hours before the start should be marked "late".
- Bookings must survive an app restart.

Keep it simple enough for me to maintain myself, and tell me how to run it.
