fix(treatment): use start date for session

src/entity/treatment/treatment_plan_session.ts

@@ -17,13 +17,15 @@ export class TreatmentPlanSession {
     @Column({ type: "date", nullable: false })
     planned_date: Date;
 
-    @Column({
-        type: "enum",
+    @Column({ type: "enum",
         enum: TreatmentSessionStatus,
         default: TreatmentSessionStatus.PLANNED,
     })
     status: TreatmentSessionStatus;
 
+    @Column({ type: "timestamp with time zone", nullable: true })
+    start_date: Date;
+
     @Column()
     @CreateDateColumn()
     created_at: Date;