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>

package.json

@@ -104,7 +104,7 @@
     "@radix-ui/react-accordion": "^1.2.4",
     "@radix-ui/react-alert-dialog": "^1.1.13",
     "@radix-ui/react-checkbox": "^1.3.2",
-    "@radix-ui/react-dialog": "^1.1.7",
+    "@radix-ui/react-dialog": "^1.1.15",
     "@radix-ui/react-dropdown-menu": "^2.1.7",
     "@radix-ui/react-label": "^2.1.4",
     "@radix-ui/react-popover": "^1.1.7",
@@ -128,6 +128,7 @@
     "better-sqlite3": "^11.9.1",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
+    "cmdk": "^1.1.1",
     "date-fns": "^4.1.0",
     "dotenv": "^16.4.7",
     "drizzle-orm": "^0.41.0",