feat: add authentik admin user sync endpoint

tests/test_internal_authentik_sync.py

@@ -0,0 +1,19 @@
+from fastapi.testclient import TestClient
+
+from app.main import app
+
+
+def test_internal_authentik_ensure_requires_config() -> None:
+    client = TestClient(app)
+    resp = client.post(
+        "/internal/authentik/users/ensure",
+        headers={"X-Internal-Secret": "CHANGE_ME"},
+        json={
+            "sub": "authentik-sub-1",
+            "email": "user@example.com",
+            "display_name": "User Example",
+            "is_active": True,
+        },
+    )
+    assert resp.status_code == 503
+    assert resp.json()["detail"] == "authentik_admin_not_configured"