Reservations — pre-book, extend, void

Reservations guarantee a spot at a specific lot/zone for a window. Customers can book online; staff can book on behalf.

To create:
1. Reservations tab → "+ New reservation"
2. Customer (contact lookup or new)
3. Lot + zone
4. Start datetime + end datetime
5. Plate (optional — speeds up entry if ALPR is wired)
6. Price computed from the zone's rate plan × duration (with any multi-day discount)
7. Payment method (charge now / charge at entry / charge at exit)
8. Save → reservation appears in the active list

Extend:
- Customer or staff hits "Extend reservation" — pick a new end time. Wally `parking_extendReservation` does it from chat. New time slot is checked against zone capacity; if the zone is full for the requested extension, alternatives in nearby zones are offered.

Void:
- "Void reservation" → reservation is cancelled. Refund follows the cancellation policy (full, partial, none) configured per lot. Wally `parking_voidSession` voids an open session if the vehicle exited without a normal close (e.g. gate malfunction).