test: migrate backend suites to pytest with module coverage gate

Split backend tests into unit and integration suites, add isolated fixtures and coverage enforcement, and update CI and test documentation. Cover current authentication, content, notification, payment, media, and admin flows; fix behaviors revealed by the new tests. Validate both suites and the per-module gate against local PostgreSQL.

core/tests/unit/test_admin.py

@@ -0,0 +1,35 @@
+from types import SimpleNamespace
+
+import pytest
+from django.contrib import admin
+
+from apps.events.models import Event
+from core.admin import BaseModelAdmin, SoftDeleteListFilter
+
+
+pytestmark = pytest.mark.unit
+
+
+def test_soft_delete_filter_selects_active_deleted_or_all(mocker):
+    filt = SoftDeleteListFilter(SimpleNamespace(GET={}), {}, Event, admin.site)
+    queryset = mocker.Mock()
+    queryset.model = Event
+    mocker.patch.object(filt, "value", return_value="0")
+    filt.queryset(None, queryset)
+    queryset.filter.assert_called_with(is_deleted=False)
+    filt.value.return_value = "1"
+    assert filt.queryset(None, queryset).model == Event
+    filt.value.return_value = None
+    assert filt.queryset(None, queryset) is queryset
+
+
+def test_admin_delete_permission_and_restore_action(mocker):
+    model_admin = BaseModelAdmin(Event, admin.site)
+    assert not model_admin.has_delete_permission(SimpleNamespace(user=SimpleNamespace(is_superuser=False)))
+    assert model_admin.has_delete_permission(SimpleNamespace(user=SimpleNamespace(is_superuser=True)))
+    mocker.patch.object(model_admin, "message_user")
+    deleted = SimpleNamespace(is_deleted=True, restore=mocker.Mock())
+    active = SimpleNamespace(is_deleted=False, restore=mocker.Mock())
+    model_admin.restore_selected(SimpleNamespace(), [deleted, active])
+    deleted.restore.assert_called_once()
+    active.restore.assert_not_called()