带有密钥的 Web 后端 (serper/brave/exa/parallel) 返回 0 个结果: 客户端日期过滤器会丢弃所有无日期的有机结果

`serper_search()` almost always returns **0 items**, even with a valid Serper API key that returns results. The Serper API responds `200` with organic results, but the client-side date filter discards every result whose `date` field is missing or unparseable — and Serper/Google rarely populates `date` on organic results. The net effect is that the Serper web backend is effectively a no-op.