- Add Search/X icons and Input to ChatConversationList with 300ms debounce
- Listen for nexus:focus-chat-search event to focus search input
- Add onSearch handler to useKeyboardShortcuts (fires before input guard)
- Wire Layout Cmd+K to open chat panel and dispatch focus event
- Add ChatConversationItem with DropdownMenu actions (Rename, Pin/Unpin, Archive, Delete) and active highlight
- Add ChatConversationList with IntersectionObserver infinite scroll, loading skeletons, delete confirmation dialog, and CRUD handlers
- Add ChatMessageList with auto-scroll-to-bottom on new messages and empty state
- Update ChatPanel to render ChatConversationList (left column) and ChatMessageList (right column); handleSend uses two paths: direct chatApi for new conversations, hook mutation for existing ones
