feat(appointment): log cancellation events and show them in a Timeline

Introduce the first per-appointment event system. On cancel (via the status
or general update endpoints) an AppointmentEvent (type=cancelled, «نوبت لغو
شد») is recorded with the actor, cancel time, and an optional cancel_reason,
plus a warning-level app_log entry. New GET /appointment/{uuid}/events
returns the ordered event list. The admin appointment detail page renders a
Timeline section and the cancel dialog now collects an optional reason.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

assets/admin/types/index.ts

@@ -116,6 +116,14 @@ export interface Appointment {
     staff?: { uuid: string; full_name: string } | null;
 }
 
+export interface AppointmentEvent {
+    type: string;
+    title: string;
+    actor_name: string | null;
+    reason: string | null;
+    created_at: number;
+}
+
 export type PaymentStatus =
     | "pending"
     | "success"