Chat search (#1224)

Based on https://github.com/dyad-sh/dyad/pull/1116
    
<!-- This is an auto-generated description by cubic. -->
---

## Summary by cubic
Adds a fast chat search dialog (Command Palette) to find and jump
between chats. Open via the sidebar button or Ctrl/Cmd+K, with title and
message text search plus inline snippets.

- New Features
  - Command palette using cmdk with keyboard shortcut (Ctrl/Cmd+K).
- Searches within the selected app across chat titles and message
content via a new IPC route (search-chats).
- Debounced queries (150ms) with React Query; results de-duplicated and
sorted by newest.
- Snippet preview with highlighted matches and custom ranking; selecting
a result navigates and closes the dialog.
- Search button added to ChatList; basic e2e tests added (currently
skipped).

- Dependencies
  - Added cmdk@1.1.1.
- Bumped @radix-ui/react-dialog to ^1.1.15 and updated Dialog to support
an optional close button.

<!-- End of auto-generated description by cubic. -->

---------

Co-authored-by: Evans Obeng <iamevansobeng@outlook.com>
Co-authored-by: Evans Obeng <60653146+iamevansobeng@users.noreply.github.com>

src/hooks/useSearchChats.ts

@@ -0,0 +1,23 @@
+import { IpcClient } from "@/ipc/ipc_client";
+import type { ChatSearchResult } from "@/lib/schemas";
+import { keepPreviousData, useQuery } from "@tanstack/react-query";
+
+export function useSearchChats(appId: number | null, query: string) {
+  const enabled = Boolean(appId && query && query.trim().length > 0);
+
+  const { data, isFetching, isLoading } = useQuery({
+    queryKey: ["search-chats", appId, query],
+    enabled,
+    queryFn: async (): Promise<ChatSearchResult[]> => {
+      // Non-null assertion safe due to enabled guard
+      return IpcClient.getInstance().searchChats(appId as number, query);
+    },
+    placeholderData: keepPreviousData,
+    retry: 0,
+  });
+
+  return {
+    chats: data ?? [],
+    loading: enabled ? isFetching || isLoading : false,
+  };
+}