feat(03-01): add SearchResults component with highlighting, scope toggle, and CommunicationHub integration

- 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

src/renderer/state/slices/communication.ts

@@ -1,10 +1,18 @@
 import type { StateCreator } from "zustand";
+import type { AgentMessageRecord } from "@shared/types";
 import type { AppState } from "../store";
 
 export interface CommunicationSlice {
-  // Placeholder for future message state -- this slice will be populated
-  // during component decomposition. The communication component currently
-  // manages its own internal state.
+  searchQuery: string;
+  searchScope: "global" | "channel";
+  searchResults: AgentMessageRecord[];
+  searchLoading: boolean;
+  searchRequestId: number;
+  setSearchQuery: (query: string) => void;
+  setSearchScope: (scope: "global" | "channel") => void;
+  setSearchResults: (results: AgentMessageRecord[], requestId: number) => void;
+  setSearchLoading: (loading: boolean) => void;
+  clearSearch: () => void;
 }
 
 export const createCommunicationSlice: StateCreator<
@@ -12,6 +20,36 @@ export const createCommunicationSlice: StateCreator<
   [["zustand/immer", never]],
   [],
   CommunicationSlice
-> = () => ({
-  // Empty state for now
+> = (set) => ({
+  searchQuery: "",
+  searchScope: "global",
+  searchResults: [],
+  searchLoading: false,
+  searchRequestId: 0,
+  setSearchQuery: (query) =>
+    set((state) => {
+      state.searchQuery = query;
+      state.searchRequestId += 1;
+    }),
+  setSearchScope: (scope) =>
+    set((state) => {
+      state.searchScope = scope;
+    }),
+  setSearchResults: (results, requestId) =>
+    set((state) => {
+      if (requestId === state.searchRequestId) {
+        state.searchResults = results;
+        state.searchLoading = false;
+      }
+    }),
+  setSearchLoading: (loading) =>
+    set((state) => {
+      state.searchLoading = loading;
+    }),
+  clearSearch: () =>
+    set((state) => {
+      state.searchQuery = "";
+      state.searchResults = [];
+      state.searchLoading = false;
+    }),
 });