Scope: Hong Kong public datasets and government data.
Fetch current HK Air Quality Health Index (AQHI) band summary from EPD.
Args: lang: "en" or "tc"
Returns {last_build_date, title, items[]} · each item has title, description, pub_date, link. Note: EPD only exposes BAND-level info (e.g. "General Stations: 3 to 4"), NOT per-station AQHI numbers. For per-station values users must visit aqhi.gov.hk directly (no API).