The Explore feed (/api/explore/item_list) is a global trending-video feed
served to anonymous sessions, and it returns the same itemStruct shape as the
other listings — so the verb reuses parse_video, the listing flow, the
TikTokVideoItem output, and the per-video billing meter wholesale. Adds a
browser-capture marker + fetch_trending, a synthetic-target orchestrator entry,
and the tiktok.trending capability, surfaced on the chat subagent.
