- Create SearchResults component with virtualized list, term highlighting via <mark>, keyboard navigation, loading/empty states
- Add search scope toggle (All Channels / This Channel) with radio group accessibility
- Integrate debounced (300ms) IPC search into CommunicationHub with stale response discard via requestId
- Update CommunicationSlice with search state (query, scope, results, loading, requestId)
- Modify FilterBar to accept scopeToggle prop and Escape key handler
- AnimatePresence cross-fade between SearchResults and MessageList views