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.

apps/users/tests/integration/test_meta.py

@@ -0,0 +1,42 @@
+import json
+
+import pytest
+
+from apps.users.models import Major, University
+
+
+pytestmark = [pytest.mark.integration, pytest.mark.django_db]
+
+
+@pytest.mark.parametrize("name,model", [("majors", Major), ("universities", University)])
+def test_meta_public_search_and_admin_lifecycle(client, user_factory, auth_headers, name, model):
+    staff = user_factory(is_staff=True)
+    admin = user_factory(is_staff=True, is_superuser=True)
+    member = user_factory()
+    path = f"/api/meta/{name}"
+    admin_path = f"/api/meta/admin/{name}"
+    assert client.get(path).status_code == 200
+    assert client.post(admin_path, data=json.dumps({"code": "TEST_META_CX", "name": "Unique Meta Choice"}),
+                       content_type="application/json", **auth_headers(member)).status_code == 403
+    created = client.post(admin_path, data=json.dumps({"code": "TEST_META_CX", "name": "Unique Meta Choice"}),
+                          content_type="application/json", **auth_headers(staff))
+    assert created.status_code == 201, created.content
+    item = model.objects.get(pk=created.json()["id"])
+    assert client.get(path, {"search": "Unique Meta Choice"}).json()["results"][0]["id"] == item.pk
+    assert client.get(path, {"search": "missing"}).json()["count"] == 0
+    assert any(row["id"] == item.pk for row in client.get(admin_path, {"search": "Unique Meta Choice"}, **auth_headers(staff)).json()["results"])
+    duplicate = client.post(admin_path, data=json.dumps({"code": "TEST_META_CX", "name": "Duplicate"}),
+                            content_type="application/json", **auth_headers(staff))
+    assert duplicate.status_code == 400
+    updated = client.put(f"{admin_path}/{item.pk}", data=json.dumps({"code": "TEST_META_CX", "name": "Updated Unique Meta Choice", "is_active": False}),
+                         content_type="application/json", **auth_headers(staff))
+    assert updated.status_code == 200, updated.content
+    item.refresh_from_db()
+    assert item.name == "Updated Unique Meta Choice" and not item.is_active
+    assert client.get(path, {"search": "TEST_META_CX"}).json()["results"] == []
+    assert client.get(admin_path, {"search": "TEST_META_CX"}, **auth_headers(staff)).json()["results"][0]["id"] == item.pk
+    assert client.delete(f"{admin_path}/{item.pk}", **auth_headers(staff)).status_code == 403
+    assert client.delete(f"{admin_path}/{item.pk}", **auth_headers(admin)).status_code == 200
+    assert model.deleted_objects.filter(pk=item.pk).exists()
+    assert client.post(f"{admin_path}/{item.pk}/restore", **auth_headers(admin)).status_code == 200
+    assert model.objects.filter(pk=item.pk).exists()