feat: add initial Django domain models

backend/checkins/admin.py

@@ -0,0 +1,17 @@
+from django.contrib import admin
+
+from .models import CheckIn
+
+
+@admin.register(CheckIn)
+class CheckInAdmin(admin.ModelAdmin):
+    list_display = ("reservation", "checked_in_at", "checked_in_by", "source", "created_at")
+    list_filter = ("source", "checked_in_at", "created_at")
+    search_fields = (
+        "reservation__name",
+        "reservation__email",
+        "reservation__performance__show__title",
+        "checked_in_by__username",
+        "checked_in_by__email",
+    )
+    readonly_fields = ("created_at", "updated_at")