Voice search, image search, and the assistant

Three new ways to search landed together: voice search (transcribe with Workers AI, then search by the transcript), image search (upload an image, get a caption and embedding, then search by meaning), and the AI assistant — a retrieval-augmented chat that cites the documents it draws its answer from, with conversation memory and streaming responses. Search rules also picked up exclusion filters and a zero-hits fallback, so a query with no matches can fall back to a recommendation model instead of an empty page.