fix(core): Ensure linked ticket models are unique

ref: #691 #681

app/core/migrations/0019_alter_ticketlinkeditem_unique_together.py

@@ -0,0 +1,17 @@
+# Generated by Django 5.1.5 on 2025-03-17 08:33
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('core', '0018_alter_ticketlinkeditem_item_type'),
+    ]
+
+    operations = [
+        migrations.AlterUniqueTogether(
+            name='ticketlinkeditem',
+            unique_together={('ticket', 'item_type', 'item')},
+        ),
+    ]

app/core/models/ticket/ticket_linked_items.py

@@ -25,6 +25,12 @@ class TicketLinkedItem(TenancyObject):
             'id'
         ]
 
+        unique_together = (
+            'ticket',
+            'item_type',
+            'item',
+        )
+
         verbose_name = 'Ticket Linked Item'
 
         verbose_name_plural = 'Ticket linked Items'