feat(chat): surface request failures as a system notice, not a judge reply

feat(confidence): match exacto de carta = alta confianza

feat(frontend): render #keyword and @card tags in chat messages

feat(frontend): render card @-tags as CardChip with hover preview in chat

feat(ui): redesign chat page with ChatGPT-style layout and visual polish

feat(ui): redesign with editorial landing page and chat interface