Fix booking creation: localStorage token, conflict detection, paid_amount

- Fix api.ts getToken/saveToken to read from localStorage (matching AuthContext) — was reading sessionStorage causing all API requests to fail auth until refresh
- Fix session cleanup on 401 to use localStorage
- Add isConflict/availableRooms helpers to BookingModal; show amber warning when selected room is occupied with clickable free room suggestions
- Pass bookings prop to BookingModal via BookingCalendar
- Add paid_amount to backend POST /bookings INSERT
- Show alert() when booking creation fails so user sees the error
- Pass paidAmount in CalendarPage handleCreate

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/components/calendar/BookingCalendar.tsx

@@ -651,6 +651,7 @@ export function BookingCalendar({ rooms, bookings, onBookingCreate, onBookingUpd
           open={true}
           draft={bookingModalDraft}
           rooms={rooms}
+          bookings={bookings}
           onClose={() => {
             if (bookingModalDraft) onDraftCancel?.(bookingModalDraft.roomId)
             setBookingModalDraft(null)