Add server dbpurgeage warning state in API and mark task complete

backend/tests/test_routers/test_server.py

@@ -68,7 +68,8 @@ def _make_settings() -> ServerSettingsResponse:
             db_path="/var/lib/fail2ban/fail2ban.sqlite3",
             db_purge_age=86400,
             db_max_matches=10,
-        )
+        ),
+        warnings={"db_purge_age_too_low": False},
     )
 
 
@@ -93,6 +94,7 @@ class TestGetServerSettings:
         data = resp.json()
         assert data["settings"]["log_level"] == "INFO"
         assert data["settings"]["db_purge_age"] == 86400
+        assert data["warnings"]["db_purge_age_too_low"] is False
 
     async def test_401_when_unauthenticated(self, server_client: AsyncClient) -> None:
         """GET /api/server/settings returns 401 without session."""