feat(waitlist): queue position on the customer manage page

A waitlisted customer saw only a bare status — worse, the badge fell
back to "Pending" for both waitlisted and cancelled states. The view
now carries a 1-based waitlistPosition (earlier-created waitlisted
bookings on the session + 1) and the page renders a warning-tone
notice with the queue spot and auto-promotion explanation, in CS/EN.
Also fixed the badge's nonexistent --danger-soft/--warning-soft tokens.

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/backend/internal/domain/models.go

@@ -458,6 +458,9 @@ type CustomerBookingView struct {
 	Location      string    `json:"location"`
 	Status        string    `json:"status"`
 	Notes         string    `json:"notes,omitempty"`
+	// WaitlistPosition is the 1-based queue spot for waitlisted class
+	// bookings; zero for any other status.
+	WaitlistPosition int `json:"waitlistPosition,omitempty"`
 }
 
 type RescheduleBookingRequest struct {