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/lib/schemas.ts

@@ -26,6 +26,24 @@ export type ChatSummary = z.infer<typeof ChatSummarySchema>;
  */
 export const ChatSummariesSchema = z.array(ChatSummarySchema);
 
+/**
+ * Zod schema for chat search result objects returned by the search-chats IPC
+ */
+export const ChatSearchResultSchema = z.object({
+  id: z.number(),
+  appId: z.number(),
+  title: z.string().nullable(),
+  createdAt: z.date(),
+  matchedMessageContent: z.string().nullable(),
+});
+
+/**
+ * Type derived from the ChatSearchResultSchema
+ */
+export type ChatSearchResult = z.infer<typeof ChatSearchResultSchema>;
+
+export const ChatSearchResultsSchema = z.array(ChatSearchResultSchema);
+
 const providers = [
   "openai",
   "anthropic",