feat(sms): implement SMS messaging and metered billing

Implement a complete SMS messaging system including:
- Integration with SMS Manager.cz API for sending messages.
- Metered billing via Stripe using monthly aggregate invoice items.
- Backend services for managing SMS settings, usage logging, and monthly reporting.
- Database migrations for tenant settings, usage logs, and monthly reports.
- Frontend dashboard components for SMS configuration, usage tracking, and history.
- Support for customer phone numbers in the booking flow.

Includes new migrations, backend services, and frontend UI components.

apps/backend/internal/bookings/service.go

@@ -122,6 +122,7 @@ func (s *Service) Create(ctx context.Context, request domain.CreateBookingReques
 
 	customerName := strings.TrimSpace(request.CustomerName)
 	customerEmail := strings.TrimSpace(request.CustomerEmail)
+	customerPhone := strings.TrimSpace(request.CustomerPhone)
 	notes := strings.TrimSpace(request.Notes)
 	if len(customerName) < 2 || len(customerName) > 120 {
 		return domain.CreateBookingResponse{}, fmt.Errorf("%w: customerName must be between 2 and 120 characters", ErrInvalidBooking)
@@ -129,6 +130,9 @@ func (s *Service) Create(ctx context.Context, request domain.CreateBookingReques
 	if _, err := mail.ParseAddress(customerEmail); err != nil {
 		return domain.CreateBookingResponse{}, fmt.Errorf("%w: customerEmail must be valid", ErrInvalidBooking)
 	}
+	if customerPhone != "" && len(customerPhone) > 30 {
+		return domain.CreateBookingResponse{}, fmt.Errorf("%w: customerPhone must be at most 30 characters", ErrInvalidBooking)
+	}
 	if len(notes) > 1000 {
 		return domain.CreateBookingResponse{}, fmt.Errorf("%w: notes must be at most 1000 characters", ErrInvalidBooking)
 	}
@@ -194,6 +198,7 @@ func (s *Service) Create(ctx context.Context, request domain.CreateBookingReques
 		BookingMode:    request.BookingMode,
 		CustomerName:   customerName,
 		CustomerEmail:  customerEmail,
+		CustomerPhone:  customerPhone,
 		StartsAt:       startsAt.UTC(),
 		EndsAt:         endsAt.UTC(),
 		Status:         status,